Some really great responses here.
Hey Nev, am sorry it's been so difficult for you. It is challenging but definitely with time it will get better. His insults and remarks to you say much, much more about him than they do about you. For anyone to need to do that to something says to me there's a deep insecurity there, either a need to put others down to elevate themself, or a need to be seen as strong and look confident to others.
Deep down it sounds like he's got some stuff, and you don't need to be the recipient of that. I know it's nice to have friends in the gym/dojo, but not everyone goes there for that reason. I never really felt like I belonged in the dojo, but I loved each and every person there. We enjoyed training together, didn't catch up outside of class, but it was still a joy to train with them. You definitely get your odd person who thinks they're better than everyone and has a real arrogance, but yeah I'm finding that putting up being treated like that just does a disservice and disrespect to yourself.
You are worth more than needing a 'friend' like that, and trust me, you will be far, far better off without him.
That's really great you feel like your anger is being lifted. If it comes up still, it's okay to have anger there. I think all too often anger gets 'shunned' and seen as wrong, with a lot of conditioning saying 'don't be angry or 'you're not supposed to feel that'. The anger is there to tell you something, and there's a truth in there somewhere. It's okay to feel that, and I recommend allowing it to come up and allowing yourself to process it. Letting go of stuff isn't about pushing it away and denying it, but in accepting it fully, and fully allowing yourself to feel it. When we repress it, it just gets locked into the system and comes out in really bizarre, unhealthy ways. Am not saying you should smack the guy hehe, but it's ok to feel, and it passes through your system properly, and to remind yourself that you are worth more than needing his friendship.
Forgiveness is in seeing that someone truly can't see what they're doing, that they're innocently not perceiving things in truth, and then overlooking their behaviour as not really personal. Then you can act from there, and choose not to tolerate that or allow others to treat you like that anymore.
Let us know how you go Nev, hope you can find joy in your training once more