Looks and Competition
It seems like you know what's up with the concern about looks. Everyone seems to have helped with that.
I was noticing, too, though, your feeling about being in competition with your husband. Naturally, we all know that this isn't the healthiest attitude but, I think, it's understandable and predictable, as well as being damn uncomfortable. If it makes you feel any better at all, if you are up for a casual fling, that is very likely to be way easier for you to accomplish than for hubby, given the differences in how men and women react to these things.
I know it's not going to be popular to say this, but, shrug, you could "go first" if you want. It might help you transition to being ok with him going on, especially once you see that you won't be left out in the cold and that you can feel attraction for someone else without it changing how you feel about your spouse. As long as you are honest about what you're doing and treat all parties with respect, I don't see that as such a bad coping mechanism even if it's not the ideal.