I'm going to start this off by saying that he's wrong. Wrong, wrong, wrong. Of course you can style your hair however you want it; it's on your head.

However, please just try to understand where he's coming from. He was attracted to you in part because you had very long hair. Now, that's completely changed. I can understand him getting upset over this, especially if he wasn't warned. Also, if he just started T five months ago...that shit is serious. It's going to make him more aggressive and loopy and life is going to be an overall shitshow until his dose is appropriate. Usually about a year in, but can take longer. This absolutely is not an excuse for his behavior, please don't misunderstand me, but it needs to be in consideration when you view his reaction. Where this should have been a normal argument, it's blown completely out of proportion. If he's never reacted this way before (and I'm assuming he hasn't), then this is probably why.

His blowing up and leaving for the night? Ok, I get it. His reactions to things are going to be way over the top for a bit until the rest of his system evens out, and it's going to take time. This should have been explained to you, which was his responsibility. He should have explained to you how difficult it was going to be to be in a relationship with him while he is transitioning. I'm assuming that he didn't. However, if he is bitching about you to his friends and they're calling you transphobic? Bye.

I'm saying 'if', because you saw something on Facebook and you can't be sure it was about you. But if he just up and left and is trash talking you, there's just no excuse for that. He shows no respect for you and he's just being selfish at this point.