I’m pretty sure James and Matthew are going to be the ‘main’ love interests in TLH. If you compare it to the other two ‘seasons’ you can see that in the TMI one Clary and Jace are in the middle and in the TID one Will, Jem and Tessa are also in the middle. I’m also willing to bet Emma and Julian are going to be in the middle in the TDA one.
I think it’s exciting and different that there’ll be a gay main character in a supernatural YA book!
Since I’m a straight guy it’ll probably be a little weird for me to read about their romance, but if there’s any author who can make you care about her characters and relationships, it’s Cassie Clare! :D I have faith in her!