LL, your first mistake was dating a girl that young and not expecting some drama. For the most part, girls between 18 and 25 do not have their heads on straight and are still in party mode. Aside from that, you stayed with this girl after she cheated on you and lied about it. You taking her back killed off any respect she had for you in the first place. You are a doormat to her. Case in point your attempt to break up with her yesterday. All she did was turn on the Niagra Falls, and you caved. This girl knows that she has you in the palm of her hand. Not to mention she works in a strip club of all places. Dude!
Last year right about this time I was dating a 22 year old girl that I met in a bar one weekend. I was 26 at the time. She worked out of town in Louisiana, and I would see her if she was coming back in town for the weekend. I was all about her because she was attractive and seemed to have her head on straight maintaining a respectable job and had goals. Well about a month into it, I pretty much figured out that she had a boyfriend in the city that she went to work in every week that she was fucking. She wasn't the best liar in the world, and I started to pick up on things that didn't add up right. Anyways, this other guy was 30 years old, and they had been dating for about 9-10 months. I waited another month or so before I had enough evidence to call her out on it one weekend when she was in town, and she owned up to everything. She didn't tell her boyfriend obviously because he was clueless, until apparently he found an email with directions to my apartment in the glovebox of her jeep. BUSTED. This guy STILL took her back after knowing that she had cheated. All I could think about was, "what a chump." Don't be that guy, LL.
If you want a decent girlfriend, find someone a little bit closer to your age. At your age, you need to be looking at girls under 25 as nothing more than "ass." If you want to upgrade them from "ass" to "girlfriend," you better have gone through a long feeling out process to make sure that it's worth your time.