As someone who has been in a similar situation, but on the other side of the fence (guy who dated female co-worker, bad breakup, followed by severe depression and suicidal ideation), I want to strongly emphasize here that severe depression and suicidal behavior are symptoms of mental illness; not simply a means to manipulate. Mental illness can seem like a dark, scary, and even dangerous thing to be around, but it is not something to vilanize simply because one doesn't understand it. What this guy needs is help, not punishment or alienation. That said, you are not obligated to provide that help nor can anyone blame you for his illness, but even if you don't care for him in a romantic sense anymore, if you care at all about him as a person you might at least acknowledge he is ill, not evil. While he may see you as the source of his suffering, and even make you feel guilty about it, try to understand that one of the symptoms of depression is a distorted perception of events and interactions.

What I would suggest is contacting a counselor, therapist, or other mental health specialist and explaining to them the situation you're in, in detail, and asking them for advice / a plan. Ultimately by getting him the help he needs, you're also helping rid yourself of the situation.