I feel very sorry for the OP; it sounds a horrible place to be in, having to go to bed with someone you don't find attractive.
Still, Brassica does have a point. If we marry somebody, surely that is on the understanding that they will age and become, to some extent, less physically attractive? Happens to even the most gorgeous hunks. And to us women too.
On the other hand, there are relationships where genuine incompatibilities emerge gradually which really do make living together virtually impossible. If you're in one of those, you probably need to cut loose.
A couple of things worry me about your post.
The first is that you seem very interested in how your partner is perceived by others, whether he is a "great catch" or not. In a good relationship, the partners are there for each other, not to show off to the world. A partner shouldn't really be about confirming your attractiveness to other people.
The second, and more worrying aspect, is that you do not mention any source of satisfaction or feeling-good-about-yourself that comes from outside your relationship with your husband. Do you have anything? Do you work? Do you have any strong interest that is your own? Is there anyone in the community you help out?
What I'm trying to get at is that your post sounds as if you are expecting happiness and fulfillment as something that your partner gives you. IME (25 happy years with dh) this isn't the way it works. While a partner can be an invaluable support when things go wrong, he can't actually give you a life all on his own; your self esteem has to come from within yourself. And as most of us live for 50 years or so after our first sexual bloom is gone, we need to base our self esteem on other things than sexual attractiveness; otherwise, it's going to be a long decline.
The first thing I would advise you to do is to have a good look at your own life. If you did move out of this marriage, how would you then try to get satisfaction? By pulling another bloke? It may happen, it may be the right thing for you, but it is unlikely to be all you need, at least in the long run. And you will be faced by the same problems of diminishing physical attractiveness.
And if you decide to stay married, you still need something more than your dh can give you.
In other words, you need to find something that makes you feel good about yourself regardless of whether you are in a relationship or not. The children are enough for some women, others may need a change of career or a really absorbing hobby.
Then I would give your marriage a chance by going to couple counselling. Surely there are tactful ways of expressing more or less what you've said in this post, without being quite so explicit about the poor guy's shortcomings?
If you need to split up, at least counselling can help you to do it in the best way. It may also help you to address your own needs. The one thing that does come across strongly in your post is that you feel a need to confirm your own value by having an attractive man. It is not just about sex being good (people can have good sex with fat, ugly, balding partners) but you want a man that confirms your attractiveness in your own eyes. Could there be anything in your past that explains this insecurity? Are there other issues that may not necessarily be about your current dh? Because if there are, they are likely to follow you into any new relationship, so they must be addressed.