Sounds like you are truly sorry for what you have done and God does forgive sexual sin. The moment you ask God to forgive you and you are sincere in your sorrow over your sin He forgives you. You will have to forgive yourself and not let the devil trip you up over guilt, you will have to resist guilt.
Look at what the bible says:
1 John 1:9
[SUP]9 [/SUP]If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
Isaiah 43:25-26
[SUP]25 [/SUP]“I, even I, am He who blots out your transgressions for My own sake; And I will not remember your sins.
[SUP]26 [/SUP]Put Me in remembrance; Let us contend together; State your case, that you may be acquitted.