Married Friend And Me

Hello,
I feel really stupid/silly to post this and I have no clue how to post it right but what the heck. Anyways, so I have this very good friend. I have known her since high school. We were like 4-5 friends always used to be together. Hanging out and having fun. She got married and now have two kids of above 10 years age . We weren't in touch because of job and all but until a year or so. So she invited me to her house and I met her houband and kids. All in all a good family.
The more I began to get in touch with her and the more I came to know she wasn't quite happy with her marriage. So as a friend, I started giving advice and support and told her everything will be alright. One day She told me she is not satisfied emotionally and sexually with her husband. She told me her husband and her sometimes don't have sex for like months. It was surprising but she told she tries but he seems always busy in work.

Then happened what shouldn't have happened at all. She asked me if I would like to do it with her. I used to like her in high school and she knew it but it was long time back. I never thought like that after all these years. I must have given her wrong signal or something i dunno. So I said that would be inappropriate and wrong couse I have a gf. I began to ignore her saying I am really busy in work and other stuff. In few friend's party i have seen her and it gets really uncomfortable. She calls and texts and i just say some random stuff and keep ignoring. I dunno what to say or do.

I think i just need help with my situation here. It is taking toll on me emotionally and I am unable to concentrate in my work. She is quite pretty and attractive. Some part of me says to do it and good part just ignores it. So far good part is dominating but i dunno that's why this post.... Give some suggestions man!! To be honest sometimes it feels to be thrilling and other i feel really guilty of even thinking that.