Please help. Dealing with suicidal bf.

We've been together (both 24) for a year, known each other since high school. When we got together he told me he was depressed but he felt better since being with me. (?) So I knew that I had to keep out for depressive signs if I saw them. Anyway, i noticed that he's depressed and suicidal lately. He tweeted that all he thinks about nowadays is death. What do I do?? I don't want to lose him. I told him he needs to see and speak to a therapist and he didn't say anything afterwards. I can't be with someone who refuses to get help, but I also don't want to feel guilty for leaving someone suicidal. Our relationship is already somewhat toxic (he's mean to me sometimes, gaslights me, very argumentative and emotionally exhausting. the list goes on.) Ive thought about leaving him already but now that he's publicly expressing his suicidal thoughts I just feel so shitty and like a horrible girlfriend. I need your advice and love ladies, please.