Issues with my child's father

Ok my child's father and I are ok with each other SOMETIMES we do tend to argue alot but we argue the most around my son's birthday. This is the second year this has happened and i am not sure what to do about this situation. So, my son's father randomly got mad at me and stayed to tell me that my son hates me, he says i do not want him and other things like this which i highly doubt because my son is only 3 years old so his father has told me i am now uninvited to my child's birthday party which we had agreed to plan together and he now says he does not want my help with anything and says my both him and my son do not want me there. All of this was yesterday (same thing happened last year) so this morning he texted me asking if i was going to sens money for my son's school i agreed because i would rather my little one be in school than at home with his dad's girlfriend (who now has her profile picture on facebook as a picture of her and my son NOT OK WITH THAT) and he will not return texts or calls when i am only asking about my little guy. I am not sure what to and would greatly appreciate any feedback