>>7232402These things can happen. Its happened to me a handful of times, really close friends disappear off the planet when they get into a relationship, if you're lucky they'll resurface in a year or so once the novelty wears off. Sometimes they never come back.
Maybe they were just lonely enough to need someone else that much.
You'll want to get angry at them for abandoning the friendship, but they won't understand the same way. So you're the person that needs to move on now.