I am going to play both sides here.
I can sort of see a way that you may not be 'cheating on her'. The issue is it is all about how one defines the word. Some people only view cheating as 'romantic' cheating. In other words it is only cheating if you are trying to have two(or more) girl/boy freinds or the ilk at once. However, many people also include that having sex with another is cheating.
So in the end I have decided to throw all that BS out the window. Cheating simply is betraying the trust of your girlfreind/boyfreind/husband/wife/etc. This throws out trying to stick a particular methodology to it. All that matters is what trusts the other has put into you. If she trusts you to be celibate cept for her, then you would be cheating. If she trusts you not to be celibate cept for her then you would not be cheating(no betrayal of trust). Etc, etc, etc...
So are you cheating? I don't konw. However, the fact that you feel the need to hide it from your current GF sounds to me like she trusts you not to have sex with others.




