I might break it down into a few subjects to think about and discuss with your husband.
1. Obviously you need to decide if you need to draw the line and tell your husband that you want to have relationships with men also, it sounds like it is something you are going to need to be happy, so that seems to be something to work on first.
2. Could having a relationship with this person have risk at your job? His being fired, you being fired, co-workers finding out and gossiping about you as if you are the town whore? Trouble finding employment afterwards if this did happen? Any other complicating factors?
3. Let's say you get the OK for #1, and you decide the risks of #2 are negligible, there's still other things that might make dating a coworker hard for your husband. For me when my husband was interested in somebody at work I was envious of thinking of them being able to slip away somewhere and make out with her in a supply closet anytime they wanted, or worried he'd end up eating lunch with her everyday, when we weren't sharing enough intimacy or time together. I'm going to guess that your husband doesn't worry as much that a woman can *gasp* be in love with another woman and so that's why it's OK, cause it's not threatening. I would probably be steering hard for #1 because if you wait until you're in love with this co-worker, presenting your case as "I want to date men because I'm already in love with this one" is going to be much more of a struggle all around.
Happiness will never come to those who fail to appreciate what they already have.