I don't know...
What kind of guy goes out with a woman on friday nights and cooks her dinner? A guy with a girlfriend? I don't think so...
OBVIOUSLY this guy is really interested in her...I can't see it any other way, but from the critics it sounds like your girlfriend won't be flying off to him, but if you read one of bush/cheney04's posts, he says that a woman can leave you if you don't push away the men that come close. And I believe it myself, from what I've heard and seen in my life and in this forum, I don't see any way of fighting this argument.
I can't tell you for sure if your girlfriend will leave you or not, but I do know that this guy likes her, alot, and if you don't do anything about it things will just get more dangerous.
Now, the next time your girlfriend calls you, maybe you should talk about it? How would she feel if a girl was going out with you on friday nights and cooking you dinner? Tell her. The reason why people do these things is because:
1: They aren't paired yet
2: They are looking (Usually when you're not looking you hang around with people of the same sexe)
3: They are interested
That's my take, watch your back.