Hello
It is tough to live with guilt and it weighs down upon you for sure. Clearly it is starting to affect your sleep and even relationship.
Guilt could sometimes be a sign of depression. Relationships often go through ups and downs. Clearly the past is not in your hand. You can work on a better present and future with your partner.
Next Steps
You can consider seeing a psychiatrist or a counsellor for discussing the issue and help. Further, if sleep troubles continue, please see them soon.
Health Tips
Remember, this too shall pass. You are lucky to have a partner who is there by your side.