If he wanted a doctor or tv anchorwoman, he would be with a doctor or tv anchorwoman.
He chose you (and you him)
If you work on it you will get over this. Very introspective about the flowers and such, these things don't quell insecurity forever. Marriage doesn't quell insecurity in some.
When you trust him fully, and that takes risk, you will feel better. I am not asserting that he is, or has done something untrustworthy at all. Rather you fear that one say he is going to pop up and say "what the hell was I thinking lets break up"! I don't think so.
I must point out that insecurity has ruined relationships. Its not easy to live with its exhausting. I don't see that you are overly insecure, but its there. I am sure he sees it every once in a while. Just keep working on it you will overcome it.