HELP ME!!! I’M FRUSTRATED , MY HUSBAND CANNOT SATISF ME IN Bed

My husband is in his mid 50s and I am 48. It’s over three years since we made love and I’ve suggested that he sees a specialist but he won’t. He shrugs that the specialist will only say that at our age, that type of thing stops. He’s not good in bed
I know that s*x is an important issue in marriage. I find myself being flippant and sarcastic with him and this leads to arguments. My husband said that if s*x meant that much to me, I should have an affair if I could find someone and that I should just be discreet about it. My husband does not satisfy me in bed.
I am considering cheating on him with someone who can satisfy me. What should I do?