Hi! Totally okay, this ask was very obviously sent in good faith even before you said so, which gives me a chance to happily yell about it, so I’m delighted!
Let’s start with what attachment is: InStar Wars and with the Jedi, it’s the concept of how you cannot hold onto someone or something so tightly because you are afraid of losing it and willing to do whatever it takes to keep it, whether that’s getting yourself killed or getting a whole lot of other people killed. If someone has a fate, you can protect them with your lightsaber, you can love them, but you can’t stop their fate (whether death or them leaving/going away from you), and going against this is going against the nature of the world. It’s literally a path to the dark side.
“[Jedi Knights] do not grow attachments, because attachment is a path to the dark side. You can love people, but you can’t want to possess them. They’re not yours. Accept that they have a fate. Even those you love most are going to die. You can’t do anything about that. Protect them with your lightsaber, but if they die they were going to die. there’s nothing you can do. All you can do is accept that fact. “In mythology, if you go to Hades to get them back you’re not doing it for them, you’re doing it for yourself. You’re doing it because you don’t want to give them up. You’re afraid to be without them. The key to the dark side is fear. You must be clean of fear, and fear of loss is the greatest fear. If you’re set up for fear of loss, you will do anything to keep that loss from happening, and you’re going to end up in the dark side. That’s the basic premise of Star Wars and the Jedi, and how it works. “That’s why they’re taken at a young age to be trained. They cannot get themselves killed trying to save their best buddy when it’s a hopeless exercise.” –George Lucas, Star Wars Archives 1999-2005
George Lucas, since the beginning, has consistently tied attachment’s context to possessive, obsessive relationships people have with things and that those feelings of attachment lead them down dark paths if they are not regulated and let go. It’s the entire story of Anakin’s fall, “ [Anakin] turns into Darth Vader because he gets attached to things.“ –George Lucas
This ties into how motivation is key for why a Jedi does something, because that’s how the Force works. If you do something because you’re afraid of losing that person, you’re afraid of living without them, then you’re connecting to the Force through fear, you’re seizing on that fear in your own mind, you’re drawing yourself closer to the dark side. If you do something truly and genuinely because you want others to be happy and free, then that is compassion and it’s the light side. Fundamentally, it’s about the feelings a Force-sensitive person feels when they do something, that’s the entire basis of how the Force works.
The Jedi speak of it in the same terms within the story as well. Anakin says that possession and attachment are forbidden, but compassion is central to their lives (Attack of the Clones). Aayla tells Ahsoka “don’t lose a thousand lives to save one” when talking about attachment to Anakin, because she doesn’t want to leave his side after he’s been injured (”Jedi Crash”). Anakin tells Ahsoka that they all struggle with attachment, when she wonders if she should have killed Barriss to prevent her from hurting the clones and Jedi and potentially millions of other people (”Brain Invaders”), etc. It’s consistently brought up in the themes of “purpose before feelings (because people will be killed otherwise) if you’re in the position the Jedi are in”.
Attachment and romantic feelings aren’t inherently the same thing in Star Wars or for the Jedi, attachment doesn’t have to be about a romantic relationship, it can be about an overzealous parent holding onto their child too long, it can be a Sith Lord’s willingness to murder anyone who gets in the way of their power, they can be willing to blow up an entire world to try to hold the galaxy in their grip. It can be running after your friends because you don’t trust them to be able to do it themselves and you are too worried about them, so you have no patience for being properly ready.
Which is why Obi-Wan reminds Anakin that romantic feelings within the Jedi Order aren’t forbidden, of course they’re allowed, they’re natural (”The Rise of Clovis”):
That all said, the Jedi do give up marriage as part of their commitment to the Jedi Order and it’s a combination of a) because they’re monks and b) their relationship with the Jedi Order is like a marriage in a lot of ways and you can’t whole-heartedly commit yourself to two paths.
If you marry someone, you should be making them your priority (setting aside political marriages or marriages of convenience, etc.) and Jedi can’t do that because they already have a higher priority. In a way, it’s similar to what attachment is, that you can’t save one life at the cost of a thousand, but it’s also not saying that marriages are inherently attachment, because it’s not like loving someone is the path to the dark side. It’s that specific concept of just what you would sacrifice for those feelings and, between their marriage to their Order and how much more difficult having a spouse or blood relative would be.
(And that they’re avoiding dynasties within the Order, like imagine if the Skywalkers were a separate family within the bigger Order, within a generation or two, they would have ALL the influential seats because the Force is just so incredibly strong in that family, they’d be on the Council, they’d get all the best positions, they’d get all the influence, it’d be so easy to not even realize how you’re favoring your sibling or your son because they share your blood.)
(In current-canon’s Dooku: Jedi Lost there’s another really good example–a Jedi on the Council secretly has a son that she brings to the Jedi Order and doesn’t tell anyone, but because she let her personal feelings cloud her judgement, she winds up being willing to do favors for the Hutt clan to get him out of his gambling debts, including some stuff that makes the Jedi Council vulnerable. Her motivations and secrecy are the problem there.)
(The example you’re thinking of above is Ki-Adi-Mundi from the Legends continuity! Because comics and books and such started coming out immediately after The Phantom Menace, they started doing worldbuilding, including a comic that had him married, since George Lucas considered that world separate from his own (the comics/novels/etc.) and let them have a good amount of free reign to do whatever. Once Attack of the Clones came out and the Jedi don’t marry, they had to scramble for a reason why he would be married, so they retconned the comics to say that he was married because male Cereans were rare and the planet had a low birth rate. This has been fairly explicitly nixed as part of the current Disney-owned Lucasfilm’s canon, Ki-Adi is not married there. But that’s why it was set up the way it was in Legends!)
Within the prequels, as far as I know, I don’t recall any Jedi being in relationships without breaking the rules (but I’m not familiar with all of Legends), but attachment and relationships aren’t quite the same thing. As Obi-Wan says, it’s not like those feelings aren’t allowed, they’re normal. But he does say that Anakin needs to make the choice to stay with the Order (and not let his relationship with Padme go that far) but this is also set during the Rush Clovis arc, where Anakin is falling into very dangerous attachment, and Obi-Wan is not unaware of Anakin’s feelings prior to this, it’s only when he sense “a deep rage” within Anakin just for mentioning Clovis’ name, that Obi-Wan says Anakin has to make a choice here (and of course he thinks the Jedi are better for Anakin).
George Lucas has also said: “Jedi Knights aren’t celibate - the thing that is forbidden is attachments - and possessive relationships.” (BBC News), furthering that the Jedi can have sex, can have romantic feelings, it’s just that they can’t devote their lives to someone in a marriage, because they already have done and a bigger duty.
So, personally, I think that if a Jedi could balance their feelings and still uphold their sacred duty, the Jedi wouldn’t really care. The Jedi aren’t actually hardcore sticklers for the letter of the law (I did a rewatch of TCW and, despite the numerous amount of times Anakin breaks the rules, not ONCE, not ONE TIME did he get in any actual trouble, because he often had good reason for it, the most he gets–when he genuinely endangers people’s lives by not wiping Artoo’s mission memory–is a scolding from Obi-Wan and then nothing), it’s about the spirit of the rule. If you’re following the spirit of it, if you’re genuinely balanced and in the light and doing your duty, they seem to be fine with you.
But, honestly, other than a handful of them, most of the Jedi just don’t even seem interested in romance, they don’t seem like it’s a thing that’s missing from their lives, they don’t seem like they’re pining for something they can’t have. It’s only a small handful that seem interested and even then they seem to want to be a Jedi more.
And for people who can feel the entire galaxy’s light in their minds, who can touch souls with other psychic space wizards or even non-psychic people, they have so much connection and warmth and love in their lives already!
