EX LET BULLDOG DIE FROM OVERHEATING, IS THIS A CASE FOR SUPERVISED VISITATION WITH KIDS?

My ex walked out on me, my one year old daughter, my two year old son, and our 4 year old english bulldog last year to be with his girlfriend. I knew that I wouldn't be able to care for the kids and dog and wanted to place the dog in a good home but my ex faught me to keep him. Today he texted me that our bulldog has died because he left him outside and he overheated. This is so unbelievably sad, because I know that my dog suffered and I am sick about it since my ex and I owned the dog together for 4 years and we knew very well that overheating would kill our dog. So we NEVER just left him outside..My ex and i live in different states and this year since we've been divorced he has seen our children for 3 days. last month he visited and stayed in my house, and left in the middle of the night a day earlier then planned without him telling me... he didn't lock the door and our 2 and 3 year old went outside to find him, which is where i found them when i woke up in the morning, OUTSIDE! the man is negligent, never calles the kids and sees them for 3 days out of the year, puts them in danger, and just killed our dog..CAN I REQUEST SUPERVISED VISITATION? I am so afraid that his negligence will result in our children being put in danger while they are in his care (the 3 days a year he decides to visit) ..of course i will contact an attorney on monday, just wondering if anyone had any advise or knowledge about this matter. Thanks.