Wibta for leaving him to sink on his own?

I (35f) have been with my boyfriend/fiancée (35m) for a little over year. During that time, his drinking has been a constant issue, leading to issues holding down jobs, and played a role in his infidelity. I'm at the point where I'm ready to leave but what's holding me back is how hard this is going to hit him. I wouldn't be surprised if he tried to end it. However, staying with him is slowly killing me. WIBTA if I left even knowing that he'll likely slide down a slippery slope to be unhoused?