Guys, TMI but it’s confused me?

I’ve been with my partner (male) for 3 nearly 4 years now. When we first met we was just “fun” sleeping together but for at least 2 months he would never finish when we had sex and I found it so bizarre it also hurt my confidence a bit🥴 so I questioned him and asked why and he just said he doesn’t know.. and still now he says he doesn’t know why he could never finish?
it isn’t a problem now but it still kind of bothers me or I feel like maybe he isn’t being completely honest or he’s hiding something from way back? Any lads have any ideas why he could never finish?

Guys, TMI but it’s confused me?
Post Opinion