Why would a nice guy do this?

i was studying abroad when i met him, everything was so good, he's a good guy he was caring and calling me everyday, he was planing for our dates with details, one night he called me and confessed he loves me truly and that he made me promise that we will fight to stay together, after that we had a date on Sunday and i went to party with my friends Saturday night, and i called him to let him know, he was so mad and started to yell i couldn't understand what he was saying because he was speaking his mother language, after that i figured it out i tried to explain, he started to ignore me, he called later to say that he's angry with me and that he's not an open minded person, after that things gone worst and he broke up with me with a msj,
we met after 2 months, i was leaving definitely and i asked him to met for the last time, he was incredibly kind and nervous, i brought him a gift with a farewell letter, and he was so touched by it that he to reach my eyes while i was looking down, then he went to stand by the window for a while and i couldn't stand the situation when my tears started to fall i left and then he ran after me and tried to stop me by hugging me while i pushed him away, he hugged me and asked for a last kiss, i couldn't say no, then he kissed my upper lip and stopped suddenly and ran while looking at me
after i went back to my country, he started to unregister and register in his account, several time... and in a week he put a picture with another girl but not sure if it was him in the pic !! and he disappeared for good
i don't understand till now... it's been 7 years now I really moved on and i have a great man by my side now, however i'm curious because i never understood all this !! i felt his love, jealousy, care... but the way he hurt me till the last day was so bad !! and i want to understand
Why would a nice guy do this?
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