Hookup said they had a Vasectomy, but pulled out?

If you can feel along the length of the Vas deferens, you should be able to find a couple of knots, one on each side of the missing tubing. If you can't find them, you will have a pretty good idea why he pulled out.

It's possible, of course, he may not welcome the examination. It's fairly personal.

Maybe he just wanted to come on your tits.

Pregnancy is just one of the risks from having unprotected sex, until you're in a committed relationship, it's sensible to use condoms.