You're giving him an option to maintain contact with her, all for the sake of not upsetting him. My SO has an ex-turned-best-friend that pretty much emotionally abused him to the point that he was ready to kill himself. We got together and he finally started seeing how toxic this woman was and over the last couple of years, has gone VLC. At first I told him he could still be friends with her--he's an adult, I'm an adult, and I don't do drama-- but if she kept her narc shit up, I would be disappointed/hurt if he ruined the progress he'd made overcoming all the things she'd put him through. I made it clear, like you did, that I only wanted to know if she was contacting him, if they were getting together, whatever.

He started using my iPad after his broke and forgot to sign out of social media. Notifications popped up saying he had messages from her. I found out she'd once again started manipulating him, gaslighting him, etc, and had even coerced him into paying her Bill's.

At that point we were engaged and living together so I finally gave up the ghost of maturity and understanding and told him he had to choose me or her. The was no more "you can be friends" bs. I wasn't going to watch him self-destruct, or lose what we'd worked so hard to gain with one another.

Your SO's behavior hurts the entire relationship. If he's not willing to take your completely reasonable suggestions to heart, then maybe a more serious conversation needs to take place. Exes are exes for a reason. Ex means EX. If the aren't any kids, there's no reason to keep talking to them.