I think he values him as a friend. He does have a girlfriend and is now married. Kami will find the right dude soon.
I think it's that he didn't realize the extent of Kami's feelings until that guy told him Kami is gay and he went and saw Kami's face as he went to give the speech. That's why he cries and wishes him happiness, he cares a lot for Kami as a friend and now realizes that he'd started up something with Kami only to get married in the end . I don't think he regrets his marriage, just that things went the way they did before he could save Kami some pain. He realized Kami's feelings now that the final piece in the puzzle, that being "he likes men", has been added and he realizes what their time together meant to Kami. He cries because he realizes he had Kami attend his wedding and that Kami is still smiling for him despite this. It all kinda clicked into place at once for him.
I know there's a sequel for Kami but somehow I also wanna know the story from that married guy's point of view..did he really realize Kami's feelings for him? Did he realize that he loves Kami back? Did he regret his wedding? Or is he happy about his wedding but still feel sad for Kami? Aaaargh I really wanna know I need a sequel for that married guy too or maybe just some extra chapters would be fine..as long as it answers all my curiosity