Maybe he was in love with his previous mate and that mate didn't want him??
If you want...
SPOILER!!!!!!
Actually, Toguto is not like that because of his previous relationship. I mean, he still thinks a lot about the other one and is hurt by the current situation, but his personality was like that from the beginning ╮(￣▽￣)╭
About his past relationship, the reason why their relationship went down the drain (although that's wrong since they were not in a relationship) was because Toguto said something bad. I mean, he didn't mean it in a bad way, but he put it in a way that left the lamb pretty much destroyed... I like Toguto but what he said (the lamb asked him if he liked him and he pretty much said that he's with him because he's a lamb, so if he was a lamb he wouldn't have stayed with him ).
Although that sounds mean and emotionless, Toguto treasures his country and always puts it before himself, that's why he said he would stay with any lamb and that's why he married Alta even if he didn't like him.
Toguto is a good guy but he also... Let's say that he is actually pretty awkward when it comes to relationships and he is REALLY bad at conveying his feelings (￣∇￣")
*if he had not been a lamb
Prince toguto is a cutie... so please tell me he isn't really mean he's just one big sack of salt ;w;; preferrably because of his previous mate