<human>: Can you give me the gist of the text in a nutshell?

Me: 21F Him: 24 Her: 24 with 3 year old child and husband

My friend, we'll call him Jack, and I "dated" for around 4 months. We had some issues, including the fact that I live over 400 miles away from him. Both of us were needy and I don't think either of us could have handled a real LDR. Fair enough. I haven't really moved on,  I still have feelings for Jack and would date him without a second thought if we lived closer to each other. 

Since Jack and I have stopped talking to each other in a romantic way, he has started "seeing" a girl who lives in his town. I remember him mentioning her before we dated, and how she was in a bad relationship with her husband and wouldn't leave. Sad story, right? Apparently the husband lives a few hours away now, for work. She still hasn't left him, has a kid with him, and all kinds of crazy baggage. But Jack keeps hanging around with her and doing nice romantic things for her. 

As a friend, I feel really compelled to confront Jack about this. I think  he is making a huge mistake and could end up very hurt, either physically, emotionally, or both. However, as someone who has had romantic interests with him in the past, I'm not sure how or even if I should approach him about this. The selfish part of me feels like I should wait it out, for him to be turned down or get confronted by the husband and then rush in and rescue him. The caring part of me wants to warn him before it's too late, but I doubt he will even listen to me because of my romantic feelings for him.
<bot>: My exboyfriend is chasing after a married woman with a child while her husband is out of town. Girl keeps promising to leave husband, but all signs point to this never happening.