Wa ‘Alaykum-us-Salaam wa Rahmatullaahi wa Barakaatuh.
1) Islam does not permit any sort of relationship before marriage. Islam forbids fornication, and all actions that could lead to it eventually, and this begins by speaking and looking. This is the unique Islamic way of destroying evil from the root.
2) He claims to love you very much, but if you are not considering marriage, it would be best for you to let go of the idea. It is worth considering, that what the youth of today see as undying love, is many a time nothing more than infatuation and puppy love. True love is the mutual feeling that Allaah creates between man and woman through the Barakah of Nikaah. You are still young, and your outlook in life, and your likes and dislikes will vastly change over the next few years. At this stage, you cannot be sure that this is what you want for life. It would be best for you to forget about him, and ask him to forget about you. If you are written for each other, let it happen at the right time, and in the right manner. Do not force your destiny to unfold before its time.
3) Your refusal of pursuing a Haraam (illicit) relationship, was the right and Islamic thing to do, which most certainly earned you the pleasure of Allaah, inshaAllaah.
4) Thinking about a non-mahram (strange) man voluntarily, is a sin. However if these thoughts come involuntarily, banish them immediately, seek forgiveness and make the Zhikr of Allaah. If you entertain them you shall be sinful.
And Allaah knows best.
A. Z. Pandor