I need help

How do I forgive myself? I made a mistake and sleep with a guy and I regret it so much, I feel like God will never forgive me and I don't forgive myself I was going through a tough time not a excuse tho. I also feel like no one will ever want me like when I get married my husband won't want me because I give it to someone else. I pray for God to forgive me but how do I forgive myself?