I have had sex with both men and women I am 18 and thoroughly enjoyed both encounters. I am starting to find that I enjoy watching gay porn and am fantasizing about men more and more. Does this mean that I am homosexual?
You are treating homosexuality as if it were a state of being, like a gender, instead of an act, which it really is. Does stealing something make a person a thief? Yes. But is he permanently a thief? There the answer depends on whether he continues to steal or not.
You have had sex with women, which is the sin of fornication. You have had sex with men, which is the sin of homosexuality. Therefore, you are guilty of both fornication and homosexuality. But whether you remain guilty of these sins depends on whether you continue them or not (I Corinthians 6:9-11).
You are reinforcing your lust for sex but watching pornography, which is also sinful (I Thessalonians 4:3-5).
But why would I stop? In God's image he has made us the way he feels is right. He gave is the choice to chose what we want to do so why am I now sinning?
God gives you the choice to steal or not to steal. Because you can steal, does it follow that you should steal? In the same way, your body is designed to have sex. God said that purpose behind that design was so you can have sex with your wife. "Let your fountain be blessed, and rejoice with the wife of your youth. As a loving deer and a graceful doe, let her breasts satisfy you at all times; and always be enraptured with her love. For why should you, my son, be enraptured by an immoral woman, and be embraced in the arms of a seductress?" (Proverbs 5:18-20). Because you can have sex with others, does this make it right? Clearly, the ability to make a choice does not mean that all choices are equally correct (Hebrews 13:4).
God gives you the ability to make choices because He wants to know who is willing to follow Him. When you choose to sin, you prove that you don't care about righteousness.
"Now therefore, fear the LORD, serve Him in sincerity and in truth, and put away the gods which your fathers served on the other side of the River and in Egypt. Serve the LORD! And if it seems evil to you to serve the LORD, choose for yourselves this day whom you will serve, whether the gods which your fathers served that were on the other side of the River, or the gods of the Amorites, in whose land you dwell. But as for me and my house, we will serve the LORD" (Joshua 24:14-15).