I'm going to blow off my date on valentine's day
That sounds rather harsh to do on Valentine's day. Did you guys have a fight?
I like to date people who are sweet, fun and full of love. And I found out he's the opposite.
It sounds like he's not a good person, so I can see why you don't want to go out with him. It might be best if you cancel so that you won't have to be unhappy.
If he changes his ways I would consider going out with him in the future.
It's fine to change your mind about people when they make personal changes for the better.