Quoting megan003:" So today he finally changed his facebook pw. We don't hang out anymore & we barely talk, plus he's ... [snip!] ... his password obviously, for a reason. like obviously i know hes an smurf ..... but my brain can't freaking process it !!!"
While your anger seems bizarre in this situation, I think I can wrap my head around it. For you, the sharing of PWs was a significant indication of intimacy. And this changing of the PW is a very clear indication that the time of intimacy with this man has officially passed.
Anger is often an outward symptom of another internal emotion. In this case that emotion revolves around hurt and loss. Its something that you just have to accept and move on from. He's not being a dick. He's moving on.
You will get through this and get over it. Once you do, you will find it much easier to attempt to maintain a co-parenting relationship with him.