The Andy Griffith Show S03 E28 The Rivals

"Nip it in the bud!"

Opie develops a case of puppy love for a girl in his class, but is crushed to find she isn't interested. Barney tries to lift his spirits by letting Opie hang out with him and Thelma Lou awhile. It works great, until Opie forgets his crush and sets his sights on Thelma Lou.