My husband cheating on me with ex girlfriend, that is currently now married [s ]

My husband has been unfaithful to me with this woman and keeps lying, refusing to admit anything. I keep finding small clues, but he continues to deny everything. Our relationship hasn't improved because he’s too focused on her. I think she's an ex-girlfriend he truly loved. They had an affair, and he never moved on from her. She hurt him deeply, and now he’s willing to risk his family for her.