Since you are a junior in high school, I think it might be a big problem. Maybe it is normal to feel attracted to her, but maybe one of those crushes that is better left alone.

Sounds like maybe she is just lonely if she is talking to you about her personal business. It doesn't sound like the healthiest stuff going on. I would probably try to chalk it up to not having someone to talk to and lack of boundaries but I don't know about the interest or intent part. Maybe distance myself from her a little for a while. It doesn't seem very appropriate for her to be discussing her marital issues with her son's high school friend to me.