Why do break-ups have to hurt so much? Why is it not so easy to move on fast when he wasn't even my type?

I was dating a guy for about 4 months and at the beginning I wasn't very interested. The first time we met we had sex and I left the same evening. I didn't think much of him, I guess he was nothing special and the sex felt average. He messaged me after and it took me 2 days to reply to him as I wasn't very interested and I was seeing someone else at that time and even had sex with another guy after him. Then he started chasing me and did a lot at the beginning to win me over. He asked to be his girlfriend after a week, he booked expensive holiday, he booked flights for Christmas to spend with his family, he said he loves me after one month. Then after he said he loves me his started giving me less and and play the bastard. I had enough and just before Christmas I broke up with him. I was fed up with always feeling I wasn't good enough for him and I didn't know what was on his mind, he was always so mysterious and I cried couple of times in my bed because he was ignoring me the whole time but when we were together he was the most loving and affectionate person. I felt I was going crazy. It's been not a month since the break-up and I don't feel like I have moved on. I cry almost every night when I am alone in my bed and I am feeling this immense pain inside and wondering how could he let me go so easily? Why did he lie that he loved me? I guess he was just using me for sex the whole time. It's really hurting me. I guess if he really loved me he wasn't gonna let me go like that. The day I broke up with him he didn't even try to understand why and he said he's tired of me constantly complaining and moaning about his behaviour. I reminisce the good moments we had together and it's really hurting me that he couldn't be the ONE. I thought we were gonna last forever. Why does it hurt when he is not even my type? How's that even possible when I was the one who took the decision to break-up and I realised I deserve much better than this guy. Why does it hurt so much then?
Why do break-ups have to hurt so much? Why is it not so easy to move on fast when he wasn't even my type?
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