He and I are both in a relationship with the same woman, Tamara and we all love each other. Falling in love with her really helped him realize that it didn't impact how he felt about me at all, and that definitely helped him overcome any lingering jealousy, but mostly he got over it by understanding that jealousy is essentially insecurity. It's fear that one has about not being good enough or being left behind or what have you. One of the great things about polyamory is that if you fall in love with someone, it doen't mean you can't still stay in other relationships. I never wanted to leave and go live with Nat. I just wanted to love him too.
We both had to do some deprogramming from monogamy-oriented ways of thinking about relationships which are based in excusivity and feeling territorial and to embrace polyamory outlook which is that love is not a pie. Giving some to one person doesn't leave less for someone else. It took some time and intention and we had a lot of very vulnerable and intimate conversations about our wants, and fears and boundaries and all of that - which had the result of brining us even closer together. This is something that is very common for poly people. I know many couple who say that going poly really strengthened their relationship for that reason, but it does take a lot of work to be that open and honest and to communicate on that high level. For us, we've found that it works really well for us, although that might not be the case for everyone.