Whatever waits for you post marriage, you will gain nothing by staying in an unhappy marriage.
It is so much better to be single than unhappily married. 1000 times better. Your marriage is sapping your confidence. I suspect that when you leave, you will start to rebuild yourself, and that will make you more confident and happier (both of which are attractive to other people).
So - even if you ended up single forever, you would still be better off ending your marriage. Once you've left you'll feel huge relief and realise what a burden you've been carrying, that's been sucking the joy out of your life.
And once single, you can take time to rebuild, to think about who you are, what you want from life, what experiences you want, where you see yourself in 5 /10 / 20 years, and start planning to make it happen.
You will be free to meet someone new if you want. And the refreshed, happy, more self-confident you will a) be less hung up on how you look, and b) will be more 'attractive' and approachable because of who you are.
Some people are obviously attractive to look at (although of course we all have different ideas of what makes physcially attractive). Some are not. But personality is worth so many times more than what your face looks like. I had a (on the face of it) v attractive bf when I was much younger. He turned out to be a cruel and selfish arse, and by the end I didn't fancy him anymore. In my memory he's not good looking at all. I've also known plenty of people who would never be described as attractive, who I find attractive because of their humour / kindness / smile / positive approach to life.
Please don't stay in an unhappy marriage. It's so much worse than being single.