We were in the same situation and tried many things.
After years, we reconsidered the idea of non-monogamy. With a lot of communication, honesty, and clear boundaries (no polyamory, no relationships with mutual friends, strict STI prevention, etc.), it turned out to be our solution.
Now, it's no longer a source of tension in our relationship, and I have one more hobby.
I'm not saying it's the solution for all couples. But it's always worth discussing things we thought were set in stone.