Example 1:
Denise: Hey, Becky, how is it going?
Becky: It's going well. Actually, I'm kind of annoyed these days.
Denise: Annoyed with what?
Becky: Well, you remember Mike, that guy I've been texting with. It's been just casual and fun but I think he's starting to catch feelings. He's really starting to become clingy, he wants to hang out all the time! He's trying to make plans for the summer time, but I doubt we'll still be talking by then. It's annoying that he thinks we're in a serious relationship.
Denise: Yeah, I see what you mean. It's always annoying when guys catch feelings when you're not interested.
Example 2:
Eddie: Good to see you, Mike! How have you been?
Mike: Hey, man! I've been great!
Eddie: You seem happy! Did you win the lottery or something?
Mike: It's better than money, bro! It's because of my special girl Becky! I think I'm in love!
Eddie: You mean Denise's friend Becky? You can't be serious. I thought you guys were just friends and only texted here and there.
Mike: Yeah, but I think this is something more. I can't stop thinking about her.
Eddie: No way, Mike! I think you're just catching feelings for her because she showed you a little bit of interest. I really don't think you should read too much into it.
Explanation:
to catch feelings is to begin to have romantic feelings for someone. This usually has negative connotations as it is unexpected or inappropriate. In example 1, Becky is annoyed that Mike is catching feelings because she believes their relationship is casual and fun. In Example 2, Eddie is trying to tell Mike that he shouldn't be thinking too seriously about their relationship. Eddie seems to be reading the situation better than Mike.
More examples:
Becky didn't mean for Mike to catch feelings.
Mike is starting to catch feelings for Becky.
Eddie thinks Mike caught feelings because Becky gave him some attention.
(Becky) I think Mike is catching feelings. I should stop replying to his texts.