I am going through all this too. But my friend is recovering and less suicidal. Still I have to listen the sadness stories of her problems. And it is correct too, there is noone else to listen. Sometimes I spent a lot of time, unnecessary hours, and I only get scolded. And if I advise something and it goes wrong, again it is scolding on me ( which gets cool down after a time) [for example, talk with your manager , don't be introvert.. I did that and he has given me more work. Talk to that other colleague , be friendly,. Now that another colleague is fighting with me or created problems because of your advices.]
Sometimes I feel I am wasting time, then I think then what type of friend I am. And when her condition is improving, I feel happy that at least I did something good in life. But her condition has improved a lot than me. ( I am not jealous, I feel, I should give time on me more) Even right now, when I am thinking to do one post, and sleep and do some work tomorrow. Her message or call can come, " today mother called and she is trying to get money from me, and doesn't love me". Then it may take one or two hours too to pacify her.
In your scenario, I think you should take his gf in confidence.