Rant time

My husband and I are having trouble from infertility to him cheating on me to money. I'm feeling so depressed so long that I'm will do anything to feel good about myself he told me that he sleeps with another women because i don't satisfy him sexually and i don't always want to have sex with him. I work a physically demanding job as I does be tried where I get home from work but he don't care I make be available for him or will to satisfy anything sexual fetish (which is to have a threesome with girls he is sleeping with) which makes me uncomfortable but I did it once to make him happy but I just made me feel worst about myself. I try talking to him about it but he call me selfish because I don't want him to be happy and I should be happy because he married me. I'm I stupid to stay in this "marriage "

Side note I'm thinking about starting an affair of my own to make myself feel good about me. I'm the end of my rope here

Please get me so advice