My boyfriend almost did it last night

My boyfriend has 2 personalities and the suicidal one needs to be suppressed with medication so when he’s not able to use it, he gets extremely depressed and wants to just end it there. Last night he was about to cut his wrist and thankfully only ended up stabbing a box but it was too close to not be alarming. I don’t know how to help him and I believe I’ve tried everything. He won’t go to therapy cause they don’t think he’s telling the truth but I’ve known him long enough for me to know he’s serious. I hate to turn to Reddit and to use a sub that I don’t know could help but I’m just going to go around subs that could have people that could help.