I recently found out that the person I have been in a relationship with for over two years has been chatting with another woman for around six months. I don’t know who she is or what she means to him, and why he never mentioned her in all the time we have been together. When I confronted him, he said he didn’t say anything because he knew I would overreact. I don’t know what to do about this, because he is not cheating on me and has only withheld this person’s presence from my life. He says she’s a friend and I should leave it at that, but I still feel betrayed and can’t really explain why. Is this a problem or am I being too possessive? Should I just let it go?
If something bothers you, and you believe you have just cause to be upset, the onus of setting your mind at ease is on your partner. For him to dismiss your concerns is insensitive and disrespectful, and he should be called out for it. The presence of a third person in any relationship is a problem if they have never been mentioned before, and his excuse isn’t valid. Honesty is critical for the building of trust, and there are deficits here because he clearly doesn’t trust you with information about some aspects of his life. Tell him why this is bothering you and insist on clarity because a loss of trust can end any relationship, irrespective of how strong you may both think it is.

My boyfriend’s best friend hates me, and I can’t seem to change his mind. Should I worry about this or just assume that it is something I can’t control?
Try speaking to your boyfriend about what his friend’s reasons are, and dismiss them if you believe you aren’t doing anything to deserve that anger. As long as your relationship with your boyfriend is strong, his friendships with other people are separate from your life and can be treated as such.