Hey hey! There can't be two of the same mindset! The world can't take two of us! =p
You sound like a fellow analytical mind... if so, I can understand that endless see-saw effect. Back and forth, back and forth, especially when regret, confusion, and self-loathing come into effect. It has gotten me in trouble because God is in the stillness; a whisper on our Spirit. And if our Spirit is too restless, if we won't let our thoughts be quiet and listen, we overlook what He's saying.
I listen to Christian music when I feel discouraged. I like all genres, but alternative rock tends to speak to me more. Some of my favorites for a situation like this are "Dear X" by Disciple; "Human" by Manafest; "Worn" by Tenth Avenue North. What kind of music do you listen to? I suggest finding a Christian radio station that you like and listening to nothing but that. I guarantee you will see a significant change by just applying God into aspects in your life, like music. Or reading the Bible daily. Or maybe a daily devotional.
Regret, shame, self-loathing, anything negative is a weapon used by the Enemy to keep us from our full potential. He takes a speck of negativity in our heart and runs with it. It's seen in the moments when you feel unworthy of God and that you need to be punished in some way for doing what you've done. Its Spiritual Warfare, and the Enemy
wants us to be weighed down. If we doubt ourselves, we can't be close to God nor do the wonderful things He has planned for us. And how dare he think he has that much control?! We are children of a mighty, loving God. And we are a threat to the Enemy! If we weren't than he wouldn't bother filling you with doubt and regret. There are many versus I've read that tells us to rejoice when struggles like this come because we are blessed.
Don't ever feel that God can't use you, sweetie. In fact, once you feel Spiritually sound and that your relationship with God has grown, I won't be surprised if God won't use this to do exactly what you sought out to do: leading other to God and by example. You will understand how these people feel, what it was like to fall into a situation like that, and you can be an example that they too can have something better. But you need to do it when God leads you to. It sounds like you need to come to terms with some things. And that's not a bad thing! What a wonderful thing it is for our Father to show us that we are worthy to be corrected! He's shown you a truth not so that you can be weighed by regret, but so that you can have a new and better life. He is molding you into a new creation, something even more precious that He can use for such wonderful things!
You have so much great potential. I don't need to know you to know that, because we all do. God know this and He will use us all in our own special way that he has planned. Our Father is standing right in front of you, waiting and speaking. You can hear it in the moment's when you said "it is easy to come back." or "I have forgiven." or "I have never left you." It was in the moment when every night you laid down and He whispered "Stop... come back to me." You felt his Words, and they were so soft, weren't they? He's in the little things.. the whispers...
Maybe you do something else that I do... I put human qualities. For instance... if I've wronged a human half as much as I've wronged God, they would have put me away, disliked me, and left me. But God doesn't work like that and we may know this, but we are so used to humans that such a loving and forgiving individual is a hard concept to grasp. It's something that I struggle with...
I'm honestly going through something similar in feeling unworthy of God, His love, and His forgiveness. We can only overcome this by seeking God and finding fellowship. So let's do our best to encourage each other so that we may be closer and more use to God!