My boyfriend has a best friend who is female. They used to date about 15 years ago which lasted around 3 months. They are now just friends( I believe this) but I find it difficult that they go on holiday together. She often stays at weekends and they also meet up at other times which I have got used to but the holidays I find hard. I’ve met her but generally I’m banned if she is around as she doesn’t want me there. Am I being unreasonable?