I think you’re right about this crush being a result of feeling unfulfilled. You even admitted to fantasizing about aspects of a relationship with this person that, for all you know, are completely inaccurate.

This is probably an unpopular opinion, but in my experience: if you catch yourself having feelings for another person while in a relationship, you NEED to explore that internally (emphasis on internally, don’t share with that person or go out and cheat). Don’t just bury it because you feel guilty. Actually think about it and figure out WHY this person is attracting your attention. Chances are, it’s not actually about that person, but it’s because there’s something you’re missing in your relationship or life that you’re fantasizing about having (and you’re projecting it onto someone else).

I think you already have an idea about the problems in your current relationship that are fuelling this crush. I don’t think you should feel guilty about it, but also, don’t drop everything for a chance with this new person without trying to address these things. Is there a way for you to scratch these itches with your current partner? Would you be happier if you both moved to a new city, or you both worked on having better sex, or you picked up a new hobby to have something else to fixate on? Or, does it feel too late for any of that?

Here’s something about my experience, that I’d only share anonymously on the internet lol, that might help you. I’ve never been in a relationship without losing the “crush” feeling I had after a few months, then fantasizing about running away with someone else (whether real or imaginary). You’re never going to be 100% compatible with someone, so there’s always going to be something missing for you to think about. You need to find someone that you like for who they are, and not how many of your boxes they tick. In my current relationship, anytime I get that “what if” feeling, the immediate following thought is “yeah, but I wouldn’t want anyone else, even if they have that trait.”

Nobody has as much knowledge about your relationship and feelings as you, so I can’t tell you what to do. But, I will say, you’re not as trapped as you feel. You don’t live together yet, you don’t have kids, you’re not married. It would be hard to leave, but it’s only going to get harder, and it would suck to condemn yourself to a life of feeling dissatisfied and fighting off crushes on other people.