I don't see a clear way of mapping the concept of a zero knowledge proof to the crush problem.

But the best I can come up with is:

1) No one learns that Alice (claims to) have a crush on Bob

2) Unless Bob also claims to have a crush on Alice, in which case.

3) Only Bob learns that Alice has a crush on him.

4) If Bob learns that Alice has a crush on him, Alice learns that Bob has a crush on her.

5) All the above guarantees are symmetric if you swap Bob and Alice.