There are many things and people that we encounter everyday that are not positive.
We are only responsible for our actions. Not those of others. When a situation like this arises we must practice compassion and accept that person or situation as part of our path and do the best we can to not let the negativity affect us.
Is it possible for you to do whatever it was today? Is the personal reason going against the Buddhas teachings?
There's no need to answer that, I was just pointing these things out.
Also remember that nothing is permanent.
You are also young and at the beginning of your path. Do your best and thats all you can do.