bf goes flaccid when using condoms

my bf has been in relationships before me and never used condoms in any of those previous relationships bc they were all on some form of bc. I told him I’d only do it with a condom and he said that was fine but he’d only ever used a condom once in his life. the other night we were about to have sex and he got the condom out. he was hard right before he put it on but immediately after he put it on, he became soft. I felt like it was my fault and felt awful. Idk what to do. I’m not having sex without condoms and I am not getting on any other birth control. condoms are the only things I will consider. he says it’s his fault because he isn’t used to condoms. I don’t know what to do. he was not getting hard with that condom on. how can I fix this?