First of all, I am very sorry for your loss. Mental illness is a very tough thing for everyone involved - the sufferer and those around him or her.
And I don't think there is any 'right' or 'wrong' response to your friend's suicide. You feel what you feel, and that is okay. You process loss the way you process loss - and if you are like most people, sometimes you even surprise yourself, in the way you cope with these sorts of situations.
As you know, I have struggled with severe clinical depression for pretty much my whole life. I'm pretty much okay when I take my 'happy pills' and keep up with my running (in truth, I think this does more for me than the meds)...but if I go off the drugs, even if everything is going well, I have to struggle to stay above water. And if I don't run for several days, I start sliding into the hole and must get on the treadmill post haste or risk things getting worse.
But like many people, in my blackest moments I have thought about ending it. And when I did, it wasn't something I WANTED to do...it was something I felt was perhaps the only remaining way out. I love my family (in particular, my sister) but they cannot fix everything...and they can't change my physiological make-up. So the struggle was not at all about hurting them. It was simply about running out of options to help myself.
I am actually glad that you are not angry at your friend, because I don't think it was his intention to hurt anyone. Likely, his intention was simply to end an intolerable level of pain, and he was down to what he genuinely believed to be his last resort. But it wouldn't be 'wrong' if you were angry with him. How you feel is simply how you feel...and you of all people know there is no 'right' and 'wrong' in that.
And I agree with your assessment that he died of Bipolar. No one WANTS to live in pain (if they do, they have other mental illness issues entirely), and no one I have ever met who struggles with bipolar, depression, or any other similar struggle wants to be that way. These illnesses make life a LOT more difficult. And life is difficult enough without the handicap of these sorts of struggles. Obviously, those who struggle never know what life would have been like if not for their own metabolisms, brain chemistry, or whatever sabotaging them. But we know this much - it would have been a lot easier. Therefore, I sort of see what happened to your friend as a sort of 'drowning' in a vat of molasses, in a way. The illness, like the molasses, makes it alot harder to keep treading...which is hard enough for 'normal' people treading regular water! And so finally, utterly exhausted, he just couldn't do it anymore. Not for lack of trying, because he tried for a very long time. But at a certain point, he just couldn't keep treading any longer. The molasses (ie, the illness) simply exhausted him earlier than treading in water would have. And in that way, the illness killed him in a very real way.
In any event, I am so very sorry for your loss...and so sorry for his family.