Step mother ask for $700

How am I wrong for being pissed off. My fiance gave his child's mother $700. She ask for it and, he simply hand it over. Apparently she needed it for "preschool" and to pay off a bill she's about to fall behind on. I get bitched at if I buy a starbucks. The kid goes to a plubic school. He didn't want to tell her no because this if the first time she has ever ask him for help. I think it's bull! The kid goes to a fucking plubic school. 700 is to pocket change. But now I'm the bitch! Wtf we are planning a wedding and fuck what I want