I'm asking my gf if she still talks to a guy she slept with before we started dating
Do you think she does?
She still keeps pictures of him, including dick pics. His is bigger.
It's normal to be jealous of a partner's ex. If she's really in touch with him and getting explicit photos from him, you should have a big talk with her about it.
Gonna have a talk with her tonight.
I see red flags all over this situation. She might still be into him if she is keeping pictures.  I hope you can have a civil conversation.