If and only if you never cheat on her again,
* don't tell her
* make sure she can never find out
* make sure it never happens again
If it happens again, you'll have to admit to yourself you're just another cheating bastard and fess up - you don't deserve her.
If you love her and don't wanna lose her - whatever the cost - well, the cost is simple: control yourself. At all times.
Oh, and just because you're not telling her, doesn't mean you don't owe her. You are in her debt, you better make up. Plan a nice romantic weekend together, buy her something nice, spoil her with romantic gifts & attention.
That might just relieve a part of your guilt, and make you feel a little more towards "deserving her" again..