Question abt positions?

So I recently lost my virginity to my current bf. Ofc I've heard that virgins are "tighter" and slowly get "looser" the more they have sex but I thought it was one of those sex-negative myths, like the one where you weren't a virgin if you didn't bleed the first time.

It seems like everytime we have sex he just can't stay in during missionary position? Like's a lot better when I'm on top (only slips out a couple times) and much, much better in doggy position, but he REALLY just.. can't make it IN when I'm under him face to face. He says I'm really, really tight but there's always foreplay so I'm always pretty lubricated? Is there anything we can do or is this position just doomed for us?