Problems having an orgasm

So the last 2-3 times my bf and I have had sex I can’t finish. It makes me feel bad bc my boyfriend thinks it’s him but it’s not! During sex I need internal and external stimulation and the D feels good but when I use my vibrator after a couple minutes it’s like my clit goes numb or something. Not numb, but it just doesn’t feel as good anymore and it doesn’t work. Hopefully that makes sense. I also feel bad bc he ends up putting like 30 minutes into it trying to make me finish and I still can’t. 😩 what is happening, what do I do.

I’m only 24 and we’ve been together for 3+ years