I'm sorry but the hard facts without trying to make you feel bad about yourself is that there are a ton of excuses in your post excusing what he does. Reread it and actively try to be honest with yourself and see if you can find them. Sometimes we just need to be hit with our own reality. I've been reading and rereading my posts trying to finding my own excuses I make for my AH and see where I'm afraid to take responsibility for what I need to do. I look at some of them and think, "I can't believe I'm allowing this to happen to my children or I".
I'm familiar with bi-polar, depression and anxiety. It's in my family to varying degrees and just like anything else, a person active in their treatment very much can be responsible for their behavior. Maybe you've just never seen anyone actively do that for themselves. So yes we can hold them accountable for owning that as well as for their addiction.
I don't mean to be hard on you. I once very much had the same mindset at your age. With 20 years passed now, I'm still sometimes wanting to revert back to that. If I could beg you not to make my mistakes I most certainly would. Don't sell yourself short and ever believe that you can fix or change or control what another person does. Don't ever believe you can save them. Don't ever take responsibility for their choices. But most of all don't ever believe that this young man is all you deserve, that he is all their is out there.
You don't know who he is when he is not an addict. What do you love because since you've met him, he's been under the control of a substance and also not treating his bi-polar. I doubt this young man knows who he is so how can he fully give to you also? This is a battle I can tell you now, doesn't have a future for you. You can care and be there as a friend if you can handle it, but aim much higher for yourself. Try to get your heart and head in line with each other. I know your hurting and am sending hugs and prayers but really, this situation is not good for you. Please don't let his addictions and problems be brought into your life.