Sanzo is a total meanie. And Goku would like to commit, he would! It's just that Sanzo's attitude makes this a very hard choice indeed. Katherine couldn't help herself, she is a politician!

Hakkai and Gojyo are not together, strictly speaking. They have something of an agreement, rather, which basically has them in this non-exclusive, but stable relationship. Too bad it wouldn't work for Sanzo and Goku... As for Hakkai being with Goku, I think I mentioned that Gojyo asked Hakkai to be Goku's first client. Just so he knew Goku was starting off well.