"the boyfriend not cumming" response

Regarding one of your answers:

"He masturbates (It's a guilt thing). If he does not, it's probably still a guilt thing you just have to talk to him and ask him what's wrong. Men are very fragile at this point. So think about it. You have not been dating that very long. It could be a old girlfriend thing ."

I'm curious about that last part "It could be a old girlfriend thing". What do you mean ??

One of his ex's could have done something that made him a little uneasy so he's not cumming right.