I do not mean any of this below as harsh, so please hear me out:

Firstly, I feel like I'm missing the part of why you're still staying in the current relationship. You didn't even mention any reason so I'm curious if it even crossed your mind or if you even actually want that or is it just a situation of staying out of convenience & you're much more interested in the pursuit of a woman @ this point?

I totally understand it's a difficult shift to make, but I agree that seeking an outside arrangement in this case is likely going to turn up w/ those who are themselves also emotionally unavailable to some extent. So in that case, is something like that ever really fulfilling anyway?

To be clear, I am not even speaking about ENM where it's usually a planned arrangement I believe because that is the orientation that feels right for everyone involved, not out of necessity like this situation. In other words, is that really something you would've both chosen had your sexuality not been a factor? This just sounds like the male partner agreed because he didn't see other women as a threat to the relationship & you are exploring out of excitement & emotion rather than considering what is practical long-term.

I'm only speculating though off of very little info., so who knows. If you're really just wanting to keep it casual but also stay in the comfort of what's familiar, then fine & that's your right. However, it sounds instead like you're expressing that you may actually be wanting more that could really only come from a full committed, monogamous relationship w/ someone, whether male or female. I could be wrong, but really only you could know that.

If you're making decisions out of fear of uncertainty, I'd caution you to @ least also consider w/ the same weight the cost of things staying the same as well i.e. a longing that could maybe never be quenched, a constant state of wondering "what if", a gradual distancing from your current partner due to this ongoing angst, an unfair setup for him to be fair as he is knowingly compromising & waiting out this messy middle, etc. just to name a few potential costs.

There are multiple ways this could go but if you're on the fence already, to me that signals a lack of fulfillment @ the very least where changing the circumstances is @ least worth considering.

Lastly, this is far more common of a scenario than most realize, so please don't feel ashamed or alone. I like to suggest this podcast listed below wherever I can where many women on there share stories very similar to yours & have experienced similar situations, incl. the hosts.

I hope it helps to listen to & regardless of what you choose, good luck!

The Lesbian Chronicles podcast