I (30F) am NM and this is a non-negociable for me. I've tried it the other way; it has never failed to make me feel miserable and trapped. My partner (39M) was not necessarily into NM when we met, but seemed totally cool with doing it with me (or was it for me?). We talked about it extensively in the early days of our relationship to make sure that we were on the same wavelength, and everything seemed more than fine.

I already had a couple of fwb when we met. He didn't - he has a very busy life and says he doesn't have much time to dedicate to the dating scene. I gently encouraged him to try and meet people, if he felt like it. He went on a few dates, but never seem too convinced. After almost every date, he told me that he only wanted me and that he didn't know how to divide his attention, how to have interest for someone else, that he doesn't know how I do it.

Then, about 2 weeks ago, he met this woman. They've been on a total of 2 dates together (within one week). He mentioned last week that meeting other people was "distracting in a bad way" (from our relationship, from me) and finally gave me more context yesterday: he told me he had developed feelings for her and that he needed to stop seeing her because it would be too dangerous for our relationship, that he wouldn't be able to control himself. It was a very long and painful discussion. He didn't want to end things with her, although it seems he knew it was his only viable option (he told me so), and he expected me to demand it from him, to force his hand.

After that, he went ahead and said that he doesn't want to take the risk of falling for someone else ever again. That he tried to be open because I stated from the very beginning that this is the only style of relationship that I want, but that it's much more difficult than he expected and that he realised he can't do it. When he sees all the uncomplicated fun I seem to have with the people I date, he is envious of me. And for this reason, because he can't do it, he wishes for me not to be open either. He wants our relationship to be exclusive, because he feels it's the only way he can remain "undistracted" from me.

I love him dearly but I don't want to end up in an exclusive relationship against my will (once again). Obviously, I can't force him into an open one either, and I don't want to lose him to the first person he'll have a crush on anyway. I also don't want him to develop negative feelings towards me, such as envy, which would happen if I kept seeing other people and he didn't.

I'm trying to approach the situation as rationally as possible, but I'm also having strong emotional reactions and I could use some advice.

I empathise with him, he's calling things off with someone he apparently deeply cares for already, and it sucks. I want to be a good partner and support to him. But I feel very threatened by the situation (he told me I only got lucky that I met him before she did, timing was on my side but basically I'm not more special to him than she is. We live together!).

After he got to the conclusion that he had to end things with her and told her through text, about 24 hours ago, she sent her a million messages. She is using textbook emotional blackmail on him, which triggers me big time, but somehow he is being extremely responsive to it, he says he can't just ignore her. They texted a lot today, even after he said he had made up his mind yesterday.

I value the fact that he opened up to me about the whole situation and I want to honour that, but I feel betrayed and disrespected, and I'm hurting a lot. And I'm afraid I'm going to suffer through yet another unhappy monogamous relationship.

Can you please help me see more clearly?

Update: Thanks everyone for you advice. He just broke up with me.