I'm going to insult the other guy
Why would you want to insult him?
I have no desire to be friends with someone who uses me
I'm sorry he's treating you like this, but there is no reason to insult him. Insults only creates animosity and more difficulties.
I'm going to still insult him. He is ungrateful. I need to call him out for acting like this.
Insults are always the sign of a weak mind and I know that you are not weak. Insulting this guy would put you in a weak place though and it is not right. Temper your statements with strong but fair words.