I have been abandoned several times when my friends got into serious relationships and/or they got married (which is especially annoying after I was a bridesmaid in their weddings, and got dropped like a hot potato immediately afterwards). I just got used to it, basically, and decided it wasn't worth my energy to hold a grudge. In a way, they do come back to you, but not quite the same as before. That significant other has become a VIP in their lives, and you really cannot begrudge them that... if it's a relationship worth anything, their spouse is going to have a much higher priority over any other type of friend, in my opinion.
However, since I've been in a serious relationship/gotten married, I've tried quite hard to maintain contact (at least online) with as many of my old friends as possible... I did not want to be a hypocrite and treat them the way they've treated me. Not everyone reciprocates, and I have to decide if I still want to be in touch with those people who are not giving back what I give to them. Most of them, though, I just like too much to let them disappear from my life... so I just keep putting in effort (which is much easier since joining Facebook, and dragging as many of my friends on there as possible). I guess I pride myself somewhat on being almost annoyingly good at keeping in touch with people... I just never give up until I get a decent reply.
