Why do I not bother asking girls out?

I am 28 years old, told I am good looking, cool to be around, etc. I am naturally shy but I have opportunities left and right to date and for some reason I dont take the initiative to ask these girls out. I was once in a 4 year relationship ..which ended badly 2 years ago. It might have something to do with this, really not sure. Anyway, I like this girl at work who I havent spoken to much but she has left obvious signs that she is interested in me. For one, she left one of my accounts on my desk with the note, "Here you go pretty eyes :)" . I go home on Fridays sometimes and think how I would like to date her or maybe someone else but I dont take the initiative. Why? She has and others have obviously given me green lights but I just choose to be alone.