Terribly depressed

I have this friend. Or I should say more then a friend. Me and him both have feeling towards eachother but have never dated and things are beyond complicated. I've known him for 2 or so years and from the very start, he has loved me and expressed a deep liking towards me. And at first I didn't like him, but now I can confidently say I love him. We go through period of happiness where we talk everyday and make eachother happy. And then sad depressing periods where we argue, and he leaves. Each time has gotten worse and worse and he leaves for longer amounts of time, but every time he comes back I'm happy aha. And it's like nothing ever went wrong. Each time he leaves, I get worse and worse mentally and I am empty now. I struggle with a lot of anxiety and depression, insomnia and self harm. I don't want to blame him for it all, but the whole experience with him has pushed me to a point. I care for him deeply, but this whole relationship just seems unhealthy and mentally abusive. I try and leave this whole thing behind and move on, but I can't. I can't seem to forget him or move on to make myself happy. I'm only 16 and I feel like life shouldn't be like this. I want desperately to be happy and find love, but this whole complicated relationship holds me back and I can't seem to escape it. I'm lost and don't know what to do