I'm mad at my fiance and friend at work
What did they do? Why are you mad?
I found out that they were planning a surprise party for me.
It's wrong to be mad at people just because you are in a bad mood. You should be happy they are planning a party for you.
They thought I would be happy about it and I'm not.
Aw, but why, they are trying to surprise you and make you have a good time! How would they feel if you didn't appreciate all of their efforts? How about putting some effort into enjoying the party, maybe you'll actually love it.