My fairly new partner has trouble staying erect through sex, we’ll be having sex for a few minutes then that’s it! It’s gone! It’s happened 4 times in a row now. I try everything to keep him hard before and after it happens and it doesn’t work yet he’s fine when I give him oral sex?

Before me he’s only had sex 3-4 times but with different people and he’s said it’s never happened before so he has no idea why. Kinda makes me feel self conscious but keeps telling me it’s not me and he also says that it isn’t the nerves (as he is inexperienced) and I’m lost on what to do as I know his confidence decreases because he gets embarrassed every time it’s happens as he just wants to please me and I just want to please him. Anything I can do to help or suggest to him that can help him out? As I can’t relate and he only wants to talk to me about it