Thanks, WhatHappened (and the other person who sent me a private message) - it really helps to know that I am not the only person to have felt like this.
Incidentally, it's a boyfriend, not a girlfriend. My boyfriend is bi, married to a gay man, and I am a straight(ish) woman (I like to joke that I just haven't met the right woman yet, haha).
I honestly think that maybe his behaviour has less to do with being poly than being simply clueless a lot of the time!
He would be appalled if he knew how much some of his behaviour, which he thinks is appropriate, has hurt me. That's why this forum has been so helpful to me.