You and your girlfriend have been together for about 3.5 months. Even though you live 90 minutes away from eachother, things are great. Your girlfriend has several male friends, which she warned you of ahead of time and reassured you that they were no threat, just friends, etc. In recent weeks, a couple of weeks a night your girlfriend has been hanging out with one guy in particular, a coworker of hers who you've been introduced to. They've been hanging out late at night, she even spent the night once (a 3rd person was there). She always tells you this up front, and doesn't try to hide things. To be fair, you too have a female friend who you hang out with, and on rare occasion spend the night at her house.
Do you get jealous? Do you think she's cheating? Does this worry you? How do you react?
Also, if you were this girl's friend, would you be concerned that she was cheating? Would you chastise her for spending time with someone other than her boyfriend? Would you advise her to stay away from this friend?