How would you deal if you felt responsible for someone's suicide?

Let’s say someone close to you commits suicide, and you feel responsible (either because you broke up with him/her, cut ties, etc). You know that it’s not completely your fault; the person was clearly unstable to begin with and had other contributing circumstances. Still, it’s hard to accept that you’re partially responsible for one’s death. How would you react? Would you break down or would you stay rational about it?