ex boyfriend! i need some serious help..

hey guys!
i'm new too this, but i realy do need some honest help & advice. I'm going to try and shorten this long and complicated story for you all..
Right, Me and this boy started talking around this time last year, we spoke alot and became friends.. we started meeting up as friends etc and got on realy well! Then i started to have feelings for him, & did me.
Thing is, i was only 14 at the time & he was 17! so the age gap was abit awkward.. we kissed etc but nothing came of 'us'. Then as soon as i turned 15 we started getting realy close.. we started going out and i realy liked him! i also lost my virginity to him. He's a realy complicated guy and i thought i understood that.. and then 6 months after we had gotten close and 2 months after we properly got together, he was in a bad mood one night, and decided he didnt feel the same for me.
As you could probly tell i was distraught & we didnt speak for a good few months! we started speaking again a few months ago and we became realy good friends! but he has now a new girlfriend. He doesnt open up to alot of people, but he tells me literally anything.. we are like bestfriends.
But! i'm still in love with him. & he knows i still have feelings for him! we speak about what happend now and then and he always says how he isnt properly over me, and how he still sees me as his, How he hates to see me with other guys and how much it cuts him up! how he thinks if him and his girlfriend broke up me & him would be straight back together and just stuff like that. -_- It's realy annoying you know, i love him so much.. as a bestfriend aswell! But :( ARGH! i dont think he gets how hard this is for me! How do you guys think he feels? honestly.. give me your truthfull awnser.
OH, and i'm seeing him on monday.. how do you think i should act!?
sorry for the essay Gaha, but i realy do need help!
thankyou, xx.

This is going to sound a bit harsh, and I apologize in advance.

He may be embarrassed to date a girl so much younger. His friends may have teased him about it, and obviously, the closer he gets to graduation or turning 18, the bigger the age gap will get.

Also, I think if he preferred you to his girlfriend, he would break up with her so he could date you again. Isn't that what YOU would do?

I think you should quit hanging out with him or you may very well end up behaving in ways you will regret later. Also, you should be really careful about having sex at your age. Many boys in that age range have the attention span of a flea, and once you sleep with them, they lose interest quickly.