My mother in law showed up high when I was giving birth AND drove a 7 year old

I am at an absolute LOSS FOR WORDS. I am so livid right now.

My fiancé and I just had a beautiful baby girl. I just got home from the hospital about a week ago. When I was in the hospital, he had his mother (who is a major addict) pick up his son to take him to the hospital to see us. His son is only 7 years old. My fiancé claimed he thought she was sober. Psh woman has never been sober for more than 5 minutes in her life. I was very out of it at the time as I was in active labor. My entire family was there and his mother showed up HIGH AS A KITE ON PILLS. She literally drove his son to the hospital and came and saw me in labor while on pills. Luckily, she didn’t actually see the baby because I hadn’t given birth yet- but she tried. I had no idea what was going on until two days after when my fiancé finally told me. I was furious. He said he yelled at his mom for endangering the life of his son, but he never made her leave. Her excuse was that she was “nervous to see my family and took something to calm her nerves”. WHAT THE HELL.

ANYWAYS. I have been an emotional mess for days because my fiancé just let her go take his son to do something completely unsupervised. We are currently in a huge fight and I am just not sure what to do. A good parent would NOT do this. I just don’t know what to do, I don’t know what to think, I feel scared for my future… He said “my mom is clean right now and she wouldn’t hurt *child*) but I’m like did she not just show up to the hospital with your son in tow, high on pills? I’m completely questioning the man I had a child with…

PLEASE give me advice and please do not come for me for not protecting his son. I do everything I can to tell my fiancé how stupid he is being and try to set as many boundaries as possible, but it always comes down to it being HIS son and HIS mother.