I have been in a very similar situation, though my spouse and I were a bit more aligned on where we wanted to be.
Looking at your situation I would say it seems if you do go back to live with your boyfriend, you would likely be stuck in that city for a while, potentially forever right? It sounds like he is pretty set on staying there. If that’s not a future that you can handle it might be best to stay in California.

At the same time, if staying in California means you might lose the love of your life, can you really live with that? Just remember there will be a point in time in your life where work and career will become less of a priority than family, especially if you do have kids. Personally, if I felt I found the one it wouldn’t even be a decision for me to be with them, I just would. But I know right now it feels like career is just as important. I would just encourage to think long-term either way.

Regardless of whatever decision you make you should tell him everything and give him a chance to say how he feels about it.