Since the two of you have only been dating for five months, consider this a bump in the road that you can get past. You confronted her, she acknowledged your feelings, expressed understanding of what she did wrong, and apologized. Now, you’re feeling like you’re jealous and worried about this other guy — I get it, and you’re not wrong. But you have to give things time to settle. You’re still relatively new in her life and he’s a friend who will fade away a little (or a lot) as your relationship with her becomes stronger. When a new relationship, like yours, forms, other relationships — family, friends, best friends — all have to jockey for position and accommodate the new relationship. Sometimes this is a graceful process and sometimes it’s not. In this case, you brought to your girlfriend’s attention, behavior she was exhibiting with a male friend, that isn’t appropriate now that she’s in a relationship with you, because it’s disrespectful and her flirtation with this other guy made you feel uncertain of what you had thought was certain. You may have to do this again. She may have to do it with you. It may not be an opposite sex friend next time, it may be her mother, or your mother, or one of your children — but you have the tools to do this and you have to allow yourself to be uncomfortable and process these relationships. They’re fluid. You’re doing great. 😉