Um no. That’s actually really unhealthy in a relationship. Being scared of losing someone can lead to jealousy and possessiveness.
What@viomma says. Because all of the obsessive love romantic nonsense aside, we need to love and be loved without that kind of fear. It’s okay to be a mindful, to treasure your lover, but don’t dread the possibility that the relationship will cease - instead enjoy it while it’s happening and remember it fondly if it ends. As Tennyson observed in Memoriam, (which was actually about a deceased friend, not a lover who split,)