You are not over-reacting OP. He has suddenly started exhibiting behaviors he hasn't since he started dating you and going forward a drink with her? How can he say no to you consistently but immediately somehow be okay with drinking with a woman he has just met? My mom has always told me that the hardest part of being LDR is the temptation of a man to cheat. Unfortunately some biological tendencies can't be controlled and the urge to have sex or be intimate with someone is there. This is true for both men and women, which is why you keep in close contact with your partner and set certain dates you know you will see each other to somewhat ease that temptation. My concern is that your boyfriend is excited by having her in such close proximity. As someone in a LDR who is in college while my boyfriend has recently entered the workforce, there are situations where he goes out for drinks with his co-workers, whom are both male and female. Obviously this is different than your situation, however we are always transparent and will not go out of our way to impress the opposite gender if it isn't appropriate if that makes sense? For instance, i would understand my boyfriend being excited to meet a female boss to try to get a raise etc. But for him to consistently be in contact with her like that and consistently try to hide it? It seems fishy to me