I dont know what to do!!!!!?

my friend jessica and her friend frank decided to pull a joke on me...which really isnt funny...frank p*ssed in my purse...and jessica knew about it...and didnt tell me....i went all day at skool with out know something was wrong...until the end of the day when i reached into my purse and got my hand wet....and then thats when i smelt it. ALL day with out knowing...and so i was going to beat franks a s s. then he told me it was jsut water...and my other friend robert told me to trust him so i did. and he didnt know the truth either. but i asked jess last night if he really did and she sed yeah. and so i got mad at her for not telling me...and now we arent talking to each other...and she sed she didnt "want to choose between friends" and that makes no sence to me...considering she didnt tell me about the purse untill i asked her...and when i asked her not to tell frank i was gonna kick his a s s for real this time she refused....what should i do???