BF going on "lads" holiday

My boyfriend of 4 years has booked a holiday to Ibiza with 4 friends. He booked it during a 2 month break we had and it hasnt bothered me since being back together until now. A friend of mines boyfriend went last summer and she has just found out he cheated on her twice while there. Its got me a little paranoid if im honest. All my boyfriends friends are single and have all cheated on girlfriends, tried to visit prostitutes while in Amsterdam while having girlfriends ect. My boyfriend also cheated on me at 20weeks pregnant (our daughter is now 18months) Ive spoke to him and he says he wouldnt cheat on me, not after working so hard to get back together during our break but i have doubts. I would never ask him to cancel but he did say he booked the holiday to get drunk and get with girls. Im just worried because he knows none of his friends would tell me if he cheated and its a slim chance i would find out. I know one of his friends will be encouraging him to cheat the whole time (its just the way he is) and with alcohol in the mix im not sure i can trust him 100%