How do I become intimate with another girl?

[Bi curious and confused]

This is a very confusing thing for me. I am a female, I am married with two kids. I have always been very, very straight. A few months ago, I became friends with a girl, who just happened to be bi-sexual. Once we really got to talking, she told me that she had a lot of feelings about me, just an attraction. I told her that was weird for me, but the more we started to talk and hang out, the more I found myself drawn to her. She is absolutely amazing. Now, here we are and I have pretty much fell in love with this girl, as she has told me she feels that same way. The confusing thing is that I am in an unhappy marriage and she is in an unhappy relationship and I think that draws us closer together as well. Now, we are all friends (even the guys). It's like we are living double lives, but I love it. She is so amazing. She is the one thing that has come in to my life and made me happy again since I have had my kids!! We flirt and everything, I just don't know how to go about anything else. We kissed once when we were by ourselves, but it wasn't very long or anything. She has been very understanding of the fact that I have never done anything like this. I just don't really know what to do. I always chicken out of just walking up behind her and holding her and kissing her neck because I'm afraid that if anything comes of it, I will choke. I don't really know what to do.
I know this sounds horrible, but regardless of this girl, I do see divorce in the near future. I love him, and I always will, but there are so many things! And, I totally agree that cheating is cheating and I do feel guilty about a simple kiss and some things we have talked about. My biggest thing is that I am just scared to make moves, scared to look like an idiot to her!