I'm with the others on this one. FI has some ladies that flirt with him at work too, and honestly, I take it as a compliment. I completely trust him and if they want to flirt with him, it just shows me that I picked a good one
I think you're going into the situation with a "guilty until proven innocent" attitude as opposed to an "innocent until proven guilty" attitude. I know you've been cheated on in the past but you can't punish your FI for this. If he's been trustworthy so far you have to trust that he will stay that way. If you don't, your relationship is really going to suffer