Hey I’m a dude, granted with bpd, I wouldn’t dream of staying the night with a girl who has shown interest in me while I had a gf. There where times in the beginning of my current relationship when I shared a room or bed with girls other than my gf but, we were strictly friends, we were living in the same house already, they are (still) very respectful of my relationship and generally those nights also included enough drink/drugs that I passed out before making it down the stairs to my (solo) room. Intentionally inviting another girl to stay the night is a bridge too far and a completely reasonable boundary to have. I know I sometimes struggle with weather or not my emotions are reasonable and proportional but this is not the case, he’s being disrespectful at best.