OK, I will give a personal experience that happened to myself earlier this year. My girlfriend doesn't care at all if I go to a strip club and the girls there feel all on me, grab me, give me lap dances or whatever. So back in February, I was at a club here in town and a girl basically did the same thing as giving me a lap dance while I was sitting at the bar. Well, my girlfriend's friend and sister walk in and see her doing this. First they walk by and say hey and act like it is no big deal. They then let it go on for another 20-30 minutes and come back and are furious. They pulled me to the side and asked what I was doing and I told them that it was no big deal because basically she is doing what the strippers do in the strip club and I didn't intend to do anything with the girl. They said the difference is strippers are paid to do it and they have no intentions in doing anything with me. The girl on the other hand isn't doing anything for money, obviously likes me, and is giving me a "I wanna f**k you grind." After this me and my girlfriend had a long talk and basically worked it out but we talked about levels of cheating as well. She said it should stop at somebody looks attractive, if it goes beyond that it is basically a form of cheating, like if I said she looks good and I wouldn't mind banging her or being her man or whatever, that is over the line. I believed that cheating could be non-physical before this event and my girlfriend pretty much agreed with my setiment.
I was thinking the same thing immediately afterward like so if I bought the girl a drink and she gave me the dance it should be no big deal, I bartered for it. I am sure it goes deeper than that though better yet I know it does.