husband cheated

caught my husband cheating. He was sleeping with his 24 year old employee . He is 33, I am 32. No children. The mistress weighs 200 pounds at least, I am 117 pounds. I am so confused, as my husband makes fun of women half her size. He says it's the biggest mistake of his life , could you ladies ever forgive this ? If so how?  We've been together since 2001, married since 2005.