Am I over reacting ?

So my s/o has been divorced since 2011 and she(ex wife) has kept his kids from him off and on since we got together in January 2014. I am now 27 weeks pregnant and she (ex wife) is being way to nice to him. I know she is up to something...just not sure what yet. (He doesn't c it thou) So today she asks him to plz pick up her brother and bring him to where she is when he picks up his son. He told her he would and I was pissed ! After everything she has done and now my s/o is gonna go out of his way for her ???!!! Hell no !!! He told her he couldn't do it but only cause I got pissed...was I wrong ?