They've known each other for 6 years. Me and my girlfriend have only been in a relationship since 8 months. She told me about her plans to watch movies with him and spending the night at his house, she also mentioned that they would be sleeping in a single bed. I already told her that I did not know how I felt about this situation. She told me not to worry since he is "no competition". So 2 days ago she stayed at his house. She doesn't seem to be concerned about my feelings at all. What do I do?