Why am i still so in love with him?

I'm 17 now but at the time I was only just 16, I went I with a guy who was 19 for almost a year and he meant everything to me and apparently I didn't to him, we broke up a lot but always got back together. A few months ago we broke up properly and a few days later he went out with the girl we broke up over as he was always so flirty with her and things. We still talk 24/7 and still care for each other a lot, we meet up a bit and he always tells me how beautiful I look and gives me hugs and acts like were still kinda going out, he still has feelings for me and I still love him loads! Whenever I talk to him or meet him I always feel so sad/heart broken and I really dislike his girlfriend even though I've never met her :/ I don't know whether I should just stay away or what? I tried to not be friends but couldn't stay away for very long that hurt even more. He said to me that he never wants to loose me as loosing me would be like loosing part of his life and that making me smile/happy make him feel good, why does he still act like this? Why do I still love him when he broke my heart?