HELP He can't finish inside

We've been married for 6 months now, and he always finishes outside (like he jerks off and finishes when we're done) he says he gets too sensitive down there and that's why he can't finish inside

I'm not gonna lie, he has done it (finish inside) but like no more than 5 times since we're been intimate

So I now he physically can but idk what's going on, and I'm concerned of what's gonna be like when we try to have kids :(