I feel so terrible about this. I have strictly been focusing on Christ for over a year now. I promised myself to wait on God until I can say "yes" to the man whom God has for me.
I started talking to this guy who presented himself as a God-fearing man. He had devotion studies with me. We spoke every day for two weeks. One day he asked to take me out. One error I did was he asked me to come to his house. I didn't think anything of it, I was very happy to see him. I don't know what came upon him, but he wanted to give me a massage, then started asking me to remove my clothes, I didn't at first, but then did. After the massage he started to touch me. I immediately fell for it. I did not have sex with him, but I fell in temptation.
The next day I told him we could not talk any more. He was fine with it. How do I go about forgiving myself and looking past this? I promised God I would protect myself. I feel like I let Him down so much.
You made several mistakes because the attack came from a direction you were not expecting to find danger.
Whether a man claims to be a Christian or not, you cannot make exceptions. You knew this man for only two weeks. You only knew what he claimed over the phone, but tells you little about him. Sure, he studied with you, but notice what Peter said about false teachers:
"But there were also false prophets among the people, even as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Lord who bought them, and bring on themselves swift destruction. ... and especially those who walk according to the flesh in the lust of uncleanness and despise authority. They are presumptuous, self-willed. They are not afraid to speak evil of dignitaries, ... and will receive the wages of unrighteousness, as those who count it pleasure to carouse in the daytime. They are spots and blemishes, carousing in their own deceptions while they feast with you, having eyes full of adultery and that cannot cease from sin, enticing unstable souls. They have a heart trained in covetous practices, and are accursed children. ... For when they speak great swelling words of emptiness, they allure through the lusts of the flesh, through lewdness, the ones who have actually escaped from those who live in error" (II Peter 2:1, 10, 13-14).
Think about it, no true Christian man would ask a woman he isn't married to take off her clothes. He would not even offer a massage because Paul said, "Now concerning the things of which you wrote to me: It is good for a man not to touch a woman" (I Corinthians 7:1). Yes, you should not have met him at his house, but even so, as soon as he tried to give you a massage, you should have been out the door.
His response to you in regards to not talking any more confirms that he was only interested in sex.
Forgiving yourself is less important than asking God for forgiveness (I John 1:9-2:1). You learned a hard lesson, so you must next change so that sin will not catch you distracted again (II Corinthians 7:10-11).