How do I handle these situations?

My boyfriend goes to therapy because he got caught cutting himself. He smokes weed when stressed and once tried to kill himself. He gets really agitated too. When he tells me this kind of stuff, i sit there quietly and think up questions to ask of what to say or do next. But its hard. Ive never had someone open up to me and especially about stuff like this. He said im the reason he stays alive and that im making him really happy. Although he still smokes weed. I asked if he was okay but he ignored it. Plus he keeps texting late. I just wonder if he is cutting himself or getting high or finding joy with someone else.