I saw my sister kissing a guy
How do you feel about her kissing him?
I'm upset. I have a problem with that guy.
You should mind your business when it comes to other people's relationships. Why are you upset about the guy?
I thought he was cute so I didn't want him to be my brother-in-law.
I understand that it can be difficult to watch a sibling develop a romance with someone you don't like or even someone you might be interested in yourself. However, your sister's relationships are her business. It would be best for your mental health to step back and not think so much about her relationship with that guy; perhaps you could think of a more constructive way to use your time.