Quote Quoting JacobR
I let the air out of his tires (I dont think that's illegal)
It is.

Quote Quoting JacobR
I honestly did it in sheer protection of my girlfriend, a sort of "stay away" kind of message, with no wanton disregard of his safety.
That's not a valid reason to spit in somebody's face. If you felt that your girlfriend was in danger, you should have gone to the police.

Consult a lawyer, and see if you may be able to negotiate a deal which would allow you to avoid a criminal conviction.