I'm was in a relationship before I got born again, which means, obviously, I was fornicating. When I newly encountered Christ, I told my boyfriend that I could no longer have sex with him based on my newly found faith. He agreed and we still continued in the relationship, which we hope would lead to marriage. After a month I fell sick, so he brought me to his mom's place, where I stayed. To cut the long story, short we had sex. He didn't want to, but I literally seduced him and he gave in. I felt bad after the act. I prayed for forgiveness and I believe God has forgiven me. Should I still tell my mentor I had sex considering the progress I made last month has gone down the drain? My mentor is not the judgemental type. I feel he will be disappointed in me and I'm ashamed.
Of course you should free ashamed in what you did. Not only did you commit fornication, but you also broke your word with your boyfriend. I assume he is not a Christian. You told him that a Christian is not to have sex before marriage, but then you seduced him when he was trying to honor your commitment to Christ. In doing this you brought reproach on the name of Christ.
Sins can be forgiven when you repent of them, so you need to get serious about your commitment to Christ. You can't have God and be worldly at the same time. "Adulterers and adulteresses! Do you not know that friendship with the world is enmity with God? Whoever therefore wants to be a friend of the world makes himself an enemy of God" (James 4:4).
There is no formal position as "mentor" in the Scriptures. There are people we trust and imitate because they are following Christ. "Brethren, join in following my example, and note those who so walk, as you have us for a pattern" (Philippians 3:17).