Ugh. I'm with you, OP. Before my husband and I started dating, I drank almost exclusively water, and hated Diet Coke. My husband drank diet coke most days, and I started taking a sip here and there when I didn't have any water handy. Eventually I developed my own habit, not quite as bad as yours; maybe 2 glasses/cans per day. I would like to kick the habit, but the constant presence of Diet Coke in the fridge (for my husband) is making it difficult. It will have to be a joint effort, probably, but I don't want to guilt or nag my husband into giving it up on my account.
I am you! This is exactly what happened to me! I know I need to give it up but I'm addicted now. I love the way it tastes and I love the carbonation. It's not so much the cans in the fridget that get me but when DH is getting one from McDonald's (they have the best!) or 7-11 (refills of any size are just $1), I think "why should I deny myself something he's enjoying". I sympathize with someone trying to kick a smoking habit but their spouse is continuing.....