I respect and appreciate your honest communication here immensely! You're clearly on one of those which I call a "steep learning curve". And that's great! What an opportunity!
We're all so different, aren't we? My love, Kevin, (12 yrs.) and I ... have a very different experience than yours. We'd be more hurt if the other had "casual" sex with someone we didn't really care about much than if either of us were to truly love another and also have that be a sexual relationship! We'd both celebrate the other's love, if that happened -- and we'd probably love to share a lover, the both of us--as in a "triangle" or "triad".
So it's funny.... I know several people who feel more hurt or (in the negative sense) "vulnerable" if their partner falls in love with another than if they "just have sex" with another. I suppose it has to do with what is called "emotional exclusivity/monogamy" as contrasted with "sexual exclusivity/monogamy". In my own case, I'd be extra, super happy if Kevin really did love another--in the full-on way. It would be good for him, so it'd be good for me. It would open him up more! Great! I'd get to bask in the glory of it. He'd not turn away from me, in that. And if he did? I don't think it likely, but if he did, I'd be ready to love another, again. It wouldn't lay me low. I've already been there. Once is enough. Well, I got cut lower when things fell apart with "R". It hurt a LOT. Still does a little. But all-in-all, a corner has been turned and I know that my primary relationship simply HAS to be with myself. My happiness cannot depend on another--but can be enhanced by another. I can only give as much to another, embrace another, forgive and love another, as I may do within myself, with myself. And I won't lose myself until the day I die.
Maybe that's why I feel so free? Because I have turned a corner, and love myself so much. Finally, after all of these years of witholding. I feel I can weather any storm. And that's the corner I have turned. I am here for me, come what will or may.
It is good here.