Me, a groomsman?

Two days ago, I got a call from the first major ex-boyfriend.  We were together for something like six years, from my senior year in college until I was 26 or so.  He was the first guy I slept with (yes, do the math.  I was ANCIENT when I lost my virginity!).  We lived together for three years, in the house i still live in.  We parted as friends, and have stayed in touch, but less so since he's moved away and gotten a new, kinda freaky-scary goth-like girlfriend.  

I tell you this because, seriously, get ready....  

He asked me to be in his wedding!

I was too taken aback to get all the details, although he promised I would not have to wear pink tulle like I did in the last wedding I was in (yes, I am STILL bitter about that).  

How completely and insanely inappropriate.  I was feeling weird about even just going to his wedding, but to be in it? Holy crap, Captain Awkward!  Its wrong for so many reasons.  First and foremost, I have already announced to all of my unmarried girlfriends that I am done being a bridesmaid.  Its not because I don't love them, its because its ridiculous at this age to get gussied up in matching satin and tulle and line up at the altar.  I just didn't know I had to announce to my guy friends that I didn't want to be a groomsman either!!  But more importantly, this is a guy I lived with, picked paint colors with and survived family holidays with.  For SIX YEARS!  Everyone in the audience would be focused on how weird it was that I was a groomsman, instead of focusing on how weird the happy couple is!  

I have to call him back and tell him no.  I feel so bad about having to say no.  I've never said no before.  I suck at saying no.  But I would suck more at being a groomsman.