I DO NOT WANT to be his friend and listen to him talk about sex and "christening an apartment - or NOT" with OW. I don't want to hear about him possibly having sex with her again! So do I just outright SAY that?
HELL YES!!!
"Look, we're still married and I'm not your B-F-F. If you want to end it with her, end it with her, but it's incredibly disrespectful to me, to our marriage and to our family for you to sit there and talk to me about 'christening' your apartment with her. Stop it."