Probably because the saiyan race is dying dead?
Probably because Bulma was the only person who cared for him, whereas everyone else called him a monster?
Probably because even though hes a jerk, hes still a person, therefore he still has hormones, and hes still a man, therefore he naturally wants a women sometime in his life
At the time, he thought the reason Goku was so strong was because he fought for others, so Vegeta had a family, thinking he'd be strong like Goku. It kinda failed, but in the end, Vegeta grew to love his family.
Wow. . .kind of like a Gaara and Naruto thing. . .fighting for others makes you stronger. . .
[EDIT]
Plus, Bulmas kind of a slut. She probably changes clothes with the door open, walks around in her underwear for no reason, and sleeps in her bra and underwear. It just so happens Vegeta was living in the same house as her for those 2 years (I think it was?).
You know even the prince of saiyans cannot deny that blaugh