Well, if you like your LTR, stay in it. If you decide that brushing up on your techniques is more important than developing your LTR, get out of it.
Most every decision we make in life comes with a consequence. The men and women who "want it all" are dreaming. Nothing in life is like that.
Sounds like you want to be a bachelor with no strings attached. Be that bachelor then. You really can't have it both ways.
However, if you want to have it both ways, toss the idea by your gf and see how she feels about it. A relationship built on deception really isn't a relationship at all.
Sorry, but in regards to LTRs and marriages, it's either or ... that is if you want to live a life of integrity and not be a 60-year old lounge lizard in the future with too much aftershave and gold chains around your neck embarrassing yourself.
Reading this board, I'm amazed at how men can't make quality, strong, ethical decisions regarding their lives. And I think a quality decision could be proclaiming one is going to be single and play around -- it's just that the men in this country are afraid to admit it. Our country has become femanized mostly because men have allowed it to be so.
Just be a man and make one of the two decisions and live with the sacrifices and consequences.