First things first: No one should EVER use a winky face in a platonic text. The winky face is like the creepy, unwanted, way-too-long hug your weird step-uncle gives you at the family holiday party. Ick and no thank you. It's like when a guy says, "Just the tip."
ANYWAY, jealousy is a major bitch. It's super toxic, all-consuming, and can ruin your relationship. Unchecked, it will creep up on you right when you think you have it under control. Something small can set it off and suddenly, you're on a roll and there ain't no comin' down.
I know the feeling all too well.
This is something I've been dealing with myself for a very long time. Your story reminds me of a time when my boyfriend's female co-worker commented "Nice beard!" on a photo of the two of us together on Facebook. Oh, I was NOT pleased. I passive-aggressively liked her comment -- and it still irks me, months later. I think the fact that it bothers me is what really bothers me, you know?
I know my partner loves me. I know that comment wasn't meant to be inappropriate or weird, but it made me feel weird. I'm not supposed to get mad at other women, but here I am getting annoyed with this girl I've never met. The only person I should be mad at is myself, which I am, because I'm insane.