My Gf hangs out with her guy friend really late at night

So my girlfriend of almost a year has made a new friend from work and they hang out after they get off and sometimes are out really late at night and sometimes she can’t go home cause she’s tired and will just crash at his place. I brought it up that I wasn’t okay with it and she told me that nothing happens that isn’t platonic and I honestly believe her. But the guy is kinda mad about it. I don’t know the guy at all so it’s not personal at all it’s just general. Also there is a 10 year age gap. 18-28. What do I do? I’m not fond with the idea of breaking up but I also don’t want to be cheated on or risk the chance of the guy trying to pull some shady stuff.