I am counting on you and I know you can do it, show faith in yourself, like I show faith in you! You should tell your sister that she shouldn't count only on your opinion but you're going to express it so she's going to be cautious, she doesn't have to break up because of your opinion, let her consider it as a warning from something you saw and that she should be careful, tell her, but tell her to keep it to herself and think about it without telling it to her boyfriend and you should tell her boyfriend that you will tell her what you want because you care about your sister and that he shouldn't be worried because in the end, your sister will make the decision.
I really don't trust him. he's dodgy. I tell my sister everything that I know about her boyfriend. actually, I shouldn't judge him. I'm a bad sister. I won't interest them any more. I don't like him, but I don't want to my sister to be sad. and they shouldn't break up because of me.