Dear [Name],
I want to start off by saying how sorry I am for deceiving you. I understand that my actions have caused you pain and distress and I regret that deeply.
I know that words cannot undo the hurt I have caused, but I want to take this opportunity to explain my behavior and apologize for it.
The truth is, I was scared. I was afraid of how you would react if I told you the truth. I was afraid of the consequences. I was afraid of being judged. I was afraid of being rejected. So, I chose to deceive you instead.
I realize now that this was a mistake. I should have been honest with you from the start. I should have trusted that you would understand and accept me for who I am. I should have had faith in our relationship.
I understand if you don't trust me anymore and if you don't want to forgive me. I understand if you want to end this relationship. All I can do is promise to be honest with you from now on and to never deceive you again.
I am truly sorry for the pain I have caused you. I hope you can find it in your heart to forgive me.
Sincerely,
[Your Name]