I can relate, because I remember your previous posts and I left my boyfriend of 5 years to be with another woman, thinking that I was a lesbian. He spent a few years hoping for something more but finally... we seem to be at a point we are both happy with - very very close platonic friends.
However, like you, where once I thought I was done with men, enlightened, blah blah... I have had confusing feelings about men over the years. Never really emotional feelings; but sexual ones.
Like you, I feel guilty, as if I am betraying my ex boyfriend. He has already told me that if I ever sleep with another man, he doesn't want to know and it would hurt him deeply, because he has concluded that we ended so that I could be with women. But... I let him believe that, through a mixture of feeling that way at the time and a little bit of what I thought was kindness.
It's true... you don't have to act on your feelings. But of course, you are having those feelings because in some part, you finally feel 'free'.... but not quite free enough to do whatever you want. So suddenly, all those other men seem tempting. Of course it's worth exploring at some point. Life is an exploration.
As for you being cool about bf and gf's poly interactions... just remember not to think of yourself as more evolved, or them being unfair, hypocritical or lagging behind. We all have our different triggers and limits. Some of that, I believe, is biological. Some of us are triggered by sight (seeing event happen)... some by sound (hearing about it)... some by language (reading what they have written to someone)... etc.
We don't feel jealousy for a number of reasons. Sometimes, we're very evolved and feel secure. I personally think it's very rare not to ever, ever, ever have even a pinprick of insecurity - a simple "well, I guess it is fathomable that my love could leave me". More likely, we are a little too self-assured, perhaps naive, narcissistic or complacent if we truly never, ever, every have a second of anything other than security. But that's my opinion. Worst case scenario... we aren't jealous because we have a deep psychological struggle with intimacy. When that's the case, we aren't as sensitive as others, so we don't feel jealousy as strongly as those who embrace intimacy, value it and are very sensitive.
Me: (29f) open poly
In a long-distance relationship with GF (39f)
Dating Descartes in my home country (27f)
“Peace comes from within. Do not seek it without." ~ Buddha