Child Custody

My ex husband (26m) and I (27f) have shared custody with our son (5m). My ex told me that he had a follow up appointment for sinitius on Tuesday (yesteday). My fiance took my son to his appointment, due to me working that day, only to find out that the appointment wasn't for sinitius, but a follow up for an ER visit. I confronted my ex (over text message. I have an active protective order against him with the stipulation that we can communicate via text in referance to our child). He did not respond. After several hours, he finally messaged me back asking how his appointment went. I continued to ask him about the ER visit and got no response at first. The he finally texted me "When I got a call from Liams teacher about him not feeling well. I took Liam to the ER after consulting with his pediatrician for him, showing symptoms of a concussion. He was a brave boy who got a CT scan, which showed no concussion but did show the sinusitis that I informed you of. Any additional details do not serve a purpose for you." I later found out through my mother, because he told her instead of me, that my son had fallen and hit his head at a trampoline park and he later started showing symptoms of a concussion at school THE NEXT DAY. I am livid and don't know what to do. I would go for full custody, but I'm scared at how that would affect my son. He loves his dad so much. Should I proceed with my gut instinct to file for custody, should I consult a lawyer? I'm so confused as to what to do here. I am out of the US