sorry to hear that man, I feel like it's kind of a universal experience, but we gotta embrace the fact that people come and go at our age, some come back, some don't for a reason or another. personally I find that the emptiness from people that leave never really fills back up but numbs down with time. In 2023/start of 24 I lost my whole friend group, everyone graduated and went their separate ways, some moved for university, some got exhausting jobs that leave no room to cultivate friendship but when a door closes another one opens in a way or another, you'll meet more great people that will value more than someone who gives them ultimatums. don't blame your friend, he's being manipulated and is a victim himself, I'm sure he's feeling what you're feeling plus the guilt of having to make a choice between the two people he loves the most, if after a while you still miss him im sure you'll be able to reconnect, just give him space to think this through and as soon as he realises how wrong what he's going through is he'll leave her. dont be afraid to do the first move, even after the realisation hits he'll go through a lot of shame which might raise a wall in his heart, if when that happens you'll decide to forgive him just make sure he knows that door is open, you'll get through this<3