Boyfriend is unable to finish during sex

My boyfriend has a hard time finishing when we have sex. He usually never does unless he jerks himself off.

Just recently he accidentally sent me a text he meant to send someone else and it had to do with our sex life. It read "Honestly I think she's just use to guys who finish within in like 2 or 3 mins. She told me I'm only the 6th guy she's been with and her last bf was 3 years before me" he quickly text me back and said "Whoops now you know I'm asking for sex advice from a friend". He says he feels bad for not being able to cum during sex but he didn't want to bring it up because he didn't want me to think it was me.

Now to me I interpreted that as it really having to do with me not performing well enough for him. I told him to not feel weird about talking to me about stuff like that and how he shouldn't feel bad about telling me what he wants sexually because I want to satisfy him in every aspect of our relationship. He made a joke about how he's glad I wasn't mad and wasn't googling ways to get away with murder. Everything I said after that he kept making a joke or ignoring my questions entirely and changing the subject. Now I left the metaphorical window wide open for the conversation to continue and him to talk to me about it but it was like he didn't want to.

This frustrates me because obviously this bugged him enough for him to want to talk to someone about it and I don't get why when I'm willing he chose to sweep it under the rug and forget about it.

Guess my question is should I be worried that he's more willing to discuss our business with someone else besides me? And is it normal for guys to not always finish or is it possible it is me and if so any advice on how to change this? I'm pretty adventurous in the bedroom and I've never had this problem with any past partners so I'm really at a lost :(