(archaic, not-comparable, slang) Foolishly infatuated with; having a romantic crush on (used with on).
"[…] You look very fit, Grannie, and Jerry says Aunt Mary is too young to be my aunt; I believe he is spoons on her already - what ho! my Uncle Jerry! Come and be introduced." 1922, Lydia Miller Middleton, The Happy Adventures:
[…] she will have grown older and wiser by that time; besides, I'm awful spoons on her—she is the sweetest little thing. 1876, The Young Ladies' Journal, page 548: