When you think your past sins are too big to be forgiven you need to remember this – nothing is bigger than my God. Certainly not any sin.
 
God will forgive you, but you have to forgive yourself. And when you do forgive yourself, use your story to help someone else out. Use your story to show how God can pull anyone out of the miry clay, spray them off, and use the beauty of their situation to reach a lost and dying world.
 
God’s bigger than your sin. He proved that on the cross. You just have to believe it. 

“If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness.” – 1 John 1:9