The end **Spoilers**

Well, the ending is left to the individual to decide. I like endings like that.
For me, I don't see Jonah taking him back. And being that they live in Los Angeles they will have plenty of space to probably not see each other very much in passing.
HOWEVER
The wedding they're going to is for the couple who had the open relationship. So obviously that couple got back together.

So you never know.

Have you see a similar movie called "In Bloom" about two young men in Chicago. Almost the same ending.. I think you'd like it a lot.