My boyfriend could've killed my ferret

I've been around animals my whole life. Chickens, goats, rabbits, horses, donkeys, you name it,I've probably had one in my house. Ever since my great grandmother died and her ferret rehomed, I've wanted one. Fourteen years later, my mother let me get my own ferret, a month before my 15th birthday. James has been with me since 9-9-16, and is my baby. He goes everywhere with me, sleeps in my bed, and follows me around the house.

My Boyfriend, who I started dating a day after I got James is one of those people who loves animals, but animals dislike him. He has severe ADHD, which causes him to be very hyper and not think about his actions, causing him to not be very gentle with James.

Today, we brought James to my grandparents house to spend the night with me here. I played with him downstairs for a few hours, then went to go make dinner. Boyfriend took over playing, then after a few minutes got bored and wanted to put James away. I told Boyfriend to put James securely in his cage, lock all of his cage doors, and close my bedroom door securely. After taking boyfriend home (hours later) I played flute downstairs for an hour, then came upstairs to find James cage door completely open, a mess made of his things, and him hiding under the bed from the cats. Boyfriend has gotten plenty of texts from me, but is asleep. James is everything to me. He's my cuddly best friend who's helped me through anything, and left unattended in my grandparents spare room could've killed him.

Should I forgive boyfriend anytime soon, and how can I make him understand how much this hurt me?

Edit: I meant to put this in another section, but I guess this works?