What does the best possible outcome look like?

I (38F) am in a relationship with my boyfriend (46M) who is married to his other partner (43F).

We had kind of a rocky start for a bunch of reasons, but ended up in a pretty decent place. I’m genuinely friends with my meta, and I’m generally happy in my relationship.

I don’t think I’m poly, in that I don’t really want to be in a romantic relationship with more than one partner at a time, but I’m not emotionally struggling with dating someone who is from a jealousy perspective.

I am struggling a little bit in a couple of places and am really hoping to hear from some people who are coming from a different place.

First, I don’t know how to picture the future best case scenario. Has anyone been in a long term poly relationship in similar circumstances? What’s the ideal? I know happy ever after isn’t a realistic mindset, but what would it even look like? Is there an element of just accepting that in most arenas, I’ll be by myself? Or something else? I don’t know what happiness could look like here, and I’m a struggling to figure out if this is what I want long term.

Second - not loving the social pressure from being in a non monogamous relationship. Do you just learn to tune out “sister wife” jokes?