My gf hasn't had her period for weeks. We have unprotected sex but i dont cum inside of her. I was wondering if she might be pregnant
It's possible. Not having her period is a sign of pregnancy. Even though you don't ejaculate you can still have precum and it may contain sperm. If you ever have inserted your penis after ejaculating there was semen, not precum, but semen with sperm in your urethra and it would have been forced into the vagina.
It only takes one sperm.
Have her take a home test. She needs to use her first morning urine for the best accuracy. Follow all directions exactly.
If negative and she's more than about 2 weeks late she should see her doctor. There can be medical reasons as to why she's not having her period.