I'm really surprised you got written warnings for what sounds to me like a minor disagreement with a colleague - but that's another matter.

It sounds like he's misinterpreted your actions and words, but on one hand he's made allegations about you which have lead to real trouble for you on the other he's more or less said he was upset with you (thinking you didn't care). It is confusing and what he did (raising a complaint) is serious.

I think moving on and chalking up to experience is the best you can do - personally I believe keeping things professional at work is the best way to avoid this kind of fall out. If you are wanting to develop friendships maybe try sports/interest groups - if things don't go well it won't impact on your career.