It sounds like you already know what to do but aren’t quite able to do it yet. That is a different thing than not knowing. You sound very clear that you do not like to be smothered by this boy, feel too controlled by him, that he makes you feel guilty, and is blaming you for his depression and suicidal thoughts. None of this is okay. The fact that he has shared that he has been suicidal changes everything. This is not healthy — and not something you can manage on your own. I would immediately talk to the guidance counselor in your high school and let him or her know that this is going on. Your friend needs help and you being nice to him because you are worried about him emotionally is an indication that he needs more help than you can give. In some ways it is like being bullied: he uses he emotions to try and control your behavior.
Please make this a priority. Your friend needs help from others. The best thing you can do as a friend is help him best by letting others know he is having thoughts of hurting himself.