I'm sorry for your loss. The death of a pet is awful.
A couple of days later he sent me a message explaining he find people crying over death hard to deal with as he lost his dad when he was younger and people crying over death brings that all back to him
Nope.
Don't even go down that route.
SO many women allow themselves to attribute shitty behaviour to some kind of childhood traumas, when it's just plain old selfishness or cruelty. A lot of men know that women are kind hearted so they will try to use that excuse if they think it will allow them to get away with fucked up behaviour.
Also, I'm afraid that if he can't behave with reasonable decency to another human being at a vulnerable and distressing time, he shouldn't be in a relationship. The reason why they do want a relationship anyway because they put their own needs first and if other people get hurt along the way, no matter!
You're sad and grieving right now, but you need to be angry because he's taken you for the kind of woman who will tolerate this kind of behaviour, which is insulting for you and worrying.
There's A LOT men out there who are in relationships because of convenience and comfort. They want a nice, warm, kind hearted woman to dote on them and provide sex, whilst they try to ensure that they have to give as little as possible in return. They regards those women as white goods, as household appliances, and when they breakdown or need maintenance (like having the audacity to be ill), it's an annoying inconvenience for them as that isn't what they signed up for.
Dump him. He will not be there for you when you need him in future.