OK this is a tuff one.. 15 years ago I met a woman who was going out with a good friend of mine.. I had done a favor for this friend and picked up her g/f at the airport.. we had never met before.. hit a lot of bars on my way back from Boston and got to know this gal and instantly found a huge attraction.. time had passed and wanted to get together with them and my friend just seemed to want to have her just for herself... I accepted this and time passed.. years went by but I had often thought about her g/f many times.. so I finally found out where she was and connected on Facebook.. we met... so excited I couldn't stand myself.. I am in an 11 year relationship with my girlfriend and she is now in a new relationship, 5 years.. we could not keep our hands off each other all night... she wanted me to meet her girlfriend so we went to her house.. as soon as the girlfriend was out of the room she kissed me and then I kissed her and apologized.. I felt bad.. we have been seeing each other since Feb 11 with the g/f present all the time except last week when we went out alone.. she got a little loaded and started to tell me she loves me and wants to be with me... called her the next morning and she said she didn't remember anything after the last drink.. I felt bad.. but this woman only answers my emails and texts when she feels like it which angers me to know end because I think I have fallen in love with her.. don't know what to do.. I want to back off but I find myself thinking about her all the time... help

It would seem that the honest thing to do would be to tell your girlfriend about the relationship and then decide how to proceed.

You can't expect this "new" person to be straight forward with you when she's cheating on her partner and you're cheating on yours.

The relationship is based on lies.

You have been in a long and committed relationship with your girl of 11 years. Although there is a strong attraction to the new person, I really think it's just that a (lustful attraction). You must ask yourself this question: Is the grass greener on the other side?

Could you stand leaving your relationship for a person who only communicates with you when she feels the need to reach out to you. Take your girl out express how much you love her and move forward from this fling of attraction that you have the other woman.

Would you want to be in a relationship feeling as though you are the person chasing the wanting of a real relationship from this person, or would you want to maintain the relationship with someone who knows you and loves you for who you are and looks forward to answering your emails and texts because you mean so much to them?

Think through it and weigh your options. Peace.

I suggest you tell your current partner what you have been up to and then end it with her. You clearly do not deserve her or her trust if you have been carrying on behind her back with another. You don't seem to be thinking this through very well. If I was given the choice of being with an honest woman who I'd been with for 11 years, or another woman who I'd met one time and fancied but she's a cheat and a flirt, well there's no competition there is there.
If you did get with this woman who you have been cheating with, what makes you think that she will not do exactly the same to you? Seems to me like she gets a thrill out of going behind her girlfriends back and you are just her play toy.
Sorry if this seems harsh, but you need a reality check. Throwing an 11 year relationship away on a whim is madness.