Zach is gay and you're his best friend, he was forced into a marriage to help with the girls financial issues when he has no attraction to her whatsoever. He actually has a crush on you.

He is standing at the end of the isle with you next to him as his best man as the bride walks down the isle

"I don't understand why I'm doing this." He whispers to you "God I'm going to vomit when I have to kiss her."