Why are thier guys like them???????????plz help me clear up my mind..?

their is this bf of mine whom i really trusted a lot.....ive done a lot for him...because i really love him....and i was really expecting that he will do the same for me....i keep on txting him even if he doesnt txt me that often...then one morning...as i have sent him a gudmorning quotes...he txted me back...and when i replied..ive also waited for his txt...and then suddenly i was greatly shock while reading his txt stating that he was in the bording house of xxxxxx and then i asked him who is that lady...then he didnt replied me back....it was lunchtime then when he txted me again..but then that was already the gurl who txted me stating that.."stop txting my bf"...and i txted her back telling her that he is also my bf.....now...im so bothered whta should i do with this kind of guy....my goodness...this is the 2nd time it happened to me....plz....help me clear up my mind......thanks.......