Can’t cum

So I’ve only ever been able to make myself cum - and can only do it with a vibrator, when me and my partner have sex it’s great and I always enjoy it and the foreplay but I’m never at the stage to cum or even the build up? No matter if he’s given head or having sex. I enjoy it but it just doesn’t get me off! I always feel bad because I want him to make me cum obviously and I know he wants me to I just can’t 😩 any tips???