Lots of good advice above. I would add that it might be helpful to you to think about how emotionally involved you want to get with your friend's marital problems. If she is an old or very close friend, of course you are already emotionally involved with her as an individual, but I have found that people in troubled marriages sometimes are very self-involved, and lean on certain friends for some pretty intense support, while offering not much in return.

Sounds really harsh, I know. But I have been that steady presence for three friends over the years, and even if you don't bad mouth the husband, which I didn't, once you know too much, the person is liable to dump you anyway. Or the husband gets uncomfortable with the friendship, even if you generally have some empathy for the guy, with the same result.

One of my oldest friends (her son was my godson) did not show up to my wedding reception because at the last minute her husband did not want to go, and they had a huge fight about it. This is her second problematic marriage, and at that moment, I was totally over her and her relationship problems. I spent half of my reception worried in the back of my mind that she or her kids had had a massively huge emergency, or were possibly killed in an accident. Have refused to talk to her since, a sad ending for a 21 year friendship.

I can count on four fingers the friends I would support considerably with no reservation if they had serious marital problems, and that is it.

Sorry to be a huge downer, but that's my experience.