be nuts about (someone or something)

1. To be very passionate and enthusiastic about something. My daughter is nuts about sports—she's currently playing soccer and tennis and taking swim lessons. A: "The kids are nuts about that drum you gave them." B: "Oh boy. Do you hate me now?" A: "Pretty much!" Tommy seems to be nuts about baseball right now, so just get him a new bat for his birthday.

2. To be very romantically interested in or in love with someone. I've seen the way Tim smiles at you—that guy is nuts about you! Of course they're nuts about each other—they've only been dating for, like, five minutes! I can tell April is totally nuts about her new boyfriend—she won't stop talking about him.

be nuts about (or on)

be very enthusiastic about or fond of. informal

1934 Dashiell Hammett The Thin Man She told me she had this job with Wynant and he was nuts about her and she was sitting pretty.