Need advise ASAP. No rude comments

Long story short mine and my husbands sex life is not good at all. We have sex one maybe twice a month and now his penis is starting to get soft. I brought up an open marriage and he said no. We tried to have sex today and it didn't happen. He said bc he loves me and wants me to be happy I can have sex w my ex. No he is not cheating on me he never has, we've been together for 7 years and I'm very happy other then sex. Help!!!!