Hazrat Ali (Radhiyallahu Anhu) wishing to marry the daughter of Abu Jahl

Q: There is a hadith about Fatima (radhiyallahu anha) being offended of Ali (radhiyallahu anhu) taking Abu Jahel's daughter as another wife. Is it because he was marrying a disbeliever or it's because of taking another wife besides her? And our Prophet (Sallallahu Alaihi Wasallam)'s saying whatever troubles Fatima (radhiyallahu anha) also troubles him. Is it about taking another wife? What teachings should we get from this hadith?

Jokingly getting married

Q: When I was in school, I had been in a relationship and for fun my friends wrote a nikaah naama which included all the details like my parents' name, witnesses, lawyer, molvi (my friends pretended to be one of the characters). It even included the mahr. Then a female friend asked us separately if we accept each other as wife and husband thrice and we both said qubool hai 3 times. I had taken it as a joke and ignored it but now after several years, an aalimah I know told me that the nikkah was done at that time and I should either immediately tell my parents about this so that the nikaah would complete or ask the guy for divorce or else I would be doing a major sin. I want to confirm if I did get married or not.