cheating, lying and a whole lot of hurt

well im 19 and my gf is 18 and we had been togethor for 2 years well back in march 2007 she cheated on me with another guy and left me and i was left with the hurt and heart ache for months because i truely do love her ....... in august out of the blue she text me and we started talking again and within 2 weeks we were back togethor and at the start of october she asked me to move in. I had a few things to sort out in my home town but the date was planned for 11th november 2007. On the night of 7th november i decided to go over and suprise her and went to her flat and sat in the lounge was 3 lads i didnt know and in the bedroom was my gf once again with a lad.... i was really upset and legged it out of there but to make things worse all 4 lads chased me and then beat me up so not only was i cut up about my gf but also i was in a strange city and hurt physically aswell...... i cant give a tip because love is a strange thing but one tip i can give is the first time they cheat just walk away and i know its hard but try not to love someone who clearly doesnt love you.