That's an easy one. Humans are not that different compared to the rest of the animal kingdom in this regard. As in... "they struggle with the idea of making big changes" - even if they're already struggling with their current human condition (a butterty job, a toxic relationship, a home place that doesn't feel like home anymore - cause of butterty neighbors and so on and so forth...), even if a change is clearly the best/recommended option. If it's something they practiced for a long time (so long that it became a part of their current personality) - that's like a new limb that's grown on them (not something one can easily remove from ones life - tho, same goes for a medium level of difficulty). Like the saying goes "better the devil you know than the devil you don't..."
When it comes to stuff like this - you have to push yourself harder and harder till you manage to swim against the tide (remove that person from your life - or remove yourself from theirs - and more importantly "keep the distance"), till you reach the calm side of the ocean, again. It's all about time and practice (keeping the distance and filling that void with something else). As mentioned in the beginning - we're not that different than animals in this regard. Once you managed to make that change (replace that image of them from your mind - with a new practice) - things will turn back to normal (so to speak). At that point - their image might even trigger bad feelings (a mental defense mechanism) - if you get in touch incidentally, so you'd prefer/wanna to keep the distance at all costs (as if they're plagued).