I Am In Love With A Straight Guy ( Need Advice, Plz Read)

Hello, I am a 15 year old guy. I am in Year 10, in the UK (Don't know what it is in other countries sorry). There is is a guy in my school who I have had a crush on since I was 13 and I am now completely in love (but not in a creepy, stalking way). In the three years I have known him I havent really talked to him I mean there has been the occasional hello but that's it really. He has a gf btw, I mention this because one day I was sitting in Chemistry class, I had finished the work that was set out for the class, so I got to do anything for the remainder of the lesson so I was absent mindingly writing his name, in quite small writing on my arm, people saw and told his gf, she confronted me about it and asked me if I fancy him, I denied it because I don't know how she would've reacted, not to mention the guy I fancy. The next night she texted me asking again if I fancied him because rumors went round again. I denied it again, but she said it was okay if I did, so I told her I did and she was very supportive about everything because she knew how I felt. The next day would be the last day of Year 9 so I was planning to tell the guy that I had a crush on him, so me and his gf was talking and she helped me figure out how to tell him how I felt about him. So the next day at dinner he walked up to me and we walked to somewhere private, he asked "What is it you wanted to tell me?" because I asked his gf to ask him to come and see me because I never know where they go because they walk around the school. At that point I was shaking and I think he could see it, I could feel my heart going at double speed, I told him that I fancied him and that I had done for a while and that I had been working up to this moment for ages and that it would be better if he heard it from me than other people. He said that he didn't mind whether I was gay, straight or bi but that he loves his gf and that he only likes me as a mate, after that the only words I could say was Thank You, we shaked hands and we went back together and left for class. Now we have had our 6 Weeks of holidays I think it was and we are back in school, and he is in some of my classes and I am crazy for him, I really wanna start talking to him more and become friends with him properly, but I am scared of what he thinks of me and that it will be awkward if I just text him randomly on facebook like hi, how are you and wuu2, but also it will be awkward if I just walk up to him randomly in school and start talking to him so I don't know the best way to approach him without making whatever he thinks of me worse or without the awkwardness, thank you if you read right to the end, I would be very grateful for any advice you could give me. Thank you :newcolor: