Double standard?

My partner (27nb) and I (26m) have had an established non-monogamous relationship ever since we started dating a few years ago. However, when I brought up wanting to explore a sexual relationship with one of my friends (26nb), they immediately refused despite all of all rules.

They did end up agreeing after all but then revoked it some time after, essentially making me feel like I have no control over my life. Cue long months of accusations, insinuations and straight up assumptions that I want my friend more than I do my partner. No matter what I said, it was shut down as not true.

They started sleeping with someone else some time ago and then agreed to let me start sleeping with my friend again. However, some time later they also started sleeping with said friend and now we're in a difficult situation. They still accuse me, insinuate that my friend is more important while doing the exact same things with them. For example I get passive agressive remarks about spending too much time with them and my partner jumps on every opportunity to see that person. I hear that I ignore my partner in favor of that friend but they get to not look at their phone for hours when they hang out. I just don't know what to do and how to navigate that. My attempts at a conversation end with me hearing that my actions make them feel unwanted but then why would they be okay if my partner does it?