I know that it's an old thread and everything is resolved by now but I'm putting in my (not very original) twopence anyway, just because.
As you mentioned, Tyler was not just your brother, he was also your best friend. He's got to miss that. I recall that Zoë was also understandably put out (figuratively as well as literally).
I'm sure that now you have it all well in hand by having a lot of special one-on-one time with both Tyler and Zoë.
Maybe Tyler will be happier when he, like Tristan, has a steady girlfriend who has become his friend as well as his lover. Then you could all watch television and sometimes go out togther. Two's company and three's a crowd but then four's company again.