My official trained service dog nicked someone and now he's banned

While waiting for a friend to pick me up from college, I was sitting in the hallway with m service dog of 3 years between my legs, leash wrapped around my leg and held in my hand. A professor (not mine) walked by me and nothing happened, she walked by again and talked to my service dog and began to stick her hand out. For some unknown reason he snaps at her without growling or barking or anything and as I yanked him back he nicks her finger. this was on footage from security cameras and she reported the incident. my dog is now banned from campus the place I need him the most. the footage looks worse then it is and there was no audio proving she talked to him. (though plenty of people have talked to him and nothing happened) ive been suicidal again since the event. I don't even want to bring him out to any other place because im so paranoid it'll happen again. my parents are divorced recently as well and my other dog has passed away without me getting to say goodbye to her a few days ago as well. everything has gotten so messed up. I don't want to be here anymore.