What's already been said. God has shown mercy to people who have spent a lot more than 18 years doing a lot worse things than you have, I guarantee it. And those same people have gone on to be great men and women of God. He doesn't condone it, but He will forgive you, and He will have mercy. It's all throughout the Bible, even in the Old Testament, before the age of grace.
I'm not gonna go into all the "you need counseling and get help" and all that stuff that everyone has already said a dozen times. I'm just gonna answer your question and leave it at that.
Yes, God is that merciful. It's all through the New Testament, go ahead and read it. It'll give you some peace and reading the Bible will be good for you.
He hath shewed thee, O man, what is good; and what doth the Lord require of thee, but to do justly, and to love mercy, and to walk humbly with thy God? -Micah 6:8 KJV
They have shewed thee, O teen, what is good; and what doth the world require of thee, but to fit in, be wealthy, have good looks, and be rebellious? -Peer Pressure 1:1
"I hate milk; it's like drinking vomit." -Edward Elric and me.
ClaecElric4God in regards to Wolfsong - You're the coolness scraped off the top of this morning's ice cream, after being pulled out of a beautiful summer day!