Unfortunately, one of them must go. It's best to remove a small twig or branch that will grow to rub against another as soon as you see it, but it sounds like it's too late for that. If one of yours is not removed, they will eventually fuse together. Take a look at the direction in which each branch is growing. If is growing back toward the center of the tree, it should be the one to go, as should any other branches/twigs growing in that direction. If neither is growing toward the center, choose the smaller or weaker one. We just relocated, and there are several myrtles with fused branches and some not yet fused, but damaged bark. Looks like you and I both have our work cut out for us.