Have I finally met 'the one', I think I have and I don't know why it's who it is?

He started working at my office 4 months ago, when he first started I literally could not stand him! I thought he was arrogant and his overall demeanor just killed me, he eventually won me over and we became good friends, recently it has turned into a romantic relationship and I can honestly say I have never felt this way about anyone before, we are actually insanely alike, we are even allergic to some of the same things, and this week when he was sick at work, it hurt so bad seeing him like that. I really see a future with him, I just cannot for the life of me figure out why first he could illicit such a negative reaction from me, and now such a positive one, he's not even my general type that I go for at all, but I am crazy about him. Any insight is appreciated!