Unsure of my relationship

I have been going out with my first girlfriend for over 2 years now and she had gone travelling by herself. I had told her i dont want to go because its just not me as i had done this when i was a kid but she had gone anyway. When she was away we were ok for the first week and after that we had too start too argue over anything i had started too hate her and started going out with friends all the time and was so happy. I had also had a crush on some other girl but never tried too hit on her because that is not me. This made me confused and i had asked her for a break because i could not do this,have a realtionship away from each other. She had asked for a break before she left and i did not want this till she had gone. She said too me that she didnt want too have a break. She had then returned home. She has been home now for a couple of months and things are not the same as they use too be. I have trouble having talking with her. She also had met a guy when she was away travelling. She has talked too him alot and she seems too get on with this guy better than me even know they only met when travelling. The guy lives 100 miles from are home town and she had gone too meet him twice once was not long after travelling were she had gone too go round the city with him the second time is too have dinner with him. She seems too be more happy with him than me and this has made me jealous and sad. I love the girl but i hate her at the moment. This has made me so confused?!? Im not sure what too think of the relationship any more. Should i end it? Can some one please give me advice?