Don't cheat. I promise you, from a victim's point of view its roughly equivalent to learning that your 2000 mother shot your dad while she was slowly grating out your veins and sitting on your chest, causing it to be impossible to breath.
My girlfriend cheated, twice. She didn't have sex either time, but 'did favours'. Each of my previous exes did the same. It's not hight on my agenda. I think I'll give the friend subtle hints, and if I pick up a response, I'll react. But 'subtle hints' never are.
Ask your GF if she has ever thought about sleeping with another woman. Usually you either get a "been there done that" if shes fun, "yeah but ive never done it" if she corruptible, or "What the hell?" if shes a dusty **** that you should leave. troof.
Stop being so selfish, if you don't like the girl your with now, you better dump her quick. Because the way it sounds, you're going to break up eventually, and the break up will be messier the longer you've been together. If you break up soon, your going to spare, not only her feelings, but yours too. Unless you're having regular sex, of course.