Going to europe with ex?

So basically, i am going to study abroad this year in italy, but i am flying to europe with my ex boyfriend since he is studying for a semester in germany. we are flying to germany and spending four nights there before parting. we made these plans before we broke up. it was a very painful breakup. we were best friends for a year before we dated, dated for six months. but it went so fast and was intense. we were each other's first loves, best friends, we said we were soul mates. however, he was always mentally unstable and little verbally abusive at times. finally, he breached my trust in may and we called it quits. however, we said we'd still be best friends and this summer we've been sleeping together and basically together but we acknowledge that we will separate next year. except, i wondering if i should try to cancel the hotel plans and try to get on another flight because today i was trying to talk to him about my trust issues and he got angry and sai di always interrogate him. and when i was crying and said i'm always there for you how come you can't be there for me. he said i should call another friend because i don't trust him and he doens't trust me and i said but you're my best friend and he sai i don't feel like youre my best friend anymore. that was so hurtful. however, i know he says hurtful things and then apologizes later and says he loves me and that he was angry. i realize this is immature and i don't want to be with this in the future but i want to have fun in europe. i'm just worried he will do something liket his right before we leave and i won't be able to cancel. advice? on how to deal? how to react with him? how to get over him? i'm so broken.