What should i do if he feels like this?

ok so i have been going out with my boyfriend for 4 months now and i spent a whole month with him on holiday. and i really love him more than anything in the world and would do anything for him but i have lost his trust for me as when we were away i was with another guy when i was drunk didn't do anything though didn't even kiss him i just sat next to him snuggled up and since then he has been cold with me. i talked to him yesterday and he said he doesn't love me anymore and hasn't ever loved me but he said he loved me before we went away and he said last night that he cared about me and fancied me but he doesn't want to be in a relationship i thought we were in a relationship but i was obviously wrong. what should i do? i cant bare to break up with him as it will break my heart as i love him so much please help me someone :'(