I don't know your religion,but i know God still loves you.All u need to do is to
1. Ask God to forgive you ur sins having realized your mistake.
2. Be closer to God who alone can make all thing right
3. Stop having an affair with her for now
4. Show love to her as christ loved u that he gave his life as a sacrifice for your sins.
5. Ask God for direction before taking your next step and I am so sure he will guide you aright.