3 year olds loving their diapers is normal.
Sometimes it can be a phase and they eventually grow out of it and sometimes they just love their diapers and may want to stay in them.
After all the child has gotten used to wearing and using their diapers and they can come to love them.
If your 3 year old is not wanting to go to the toilet and wants his diapers I would simply back off of the potty training for a few months and try again.
Don't force the issue but still offer the toilet for him to go in.
Eventually he may decide that he wants to use the toilet but 3 years old is normal to be wearing diapers and not be toilet trained.
Children don't really need potty training as they will go to the toilet when they want too.
Diapers are not harming the child so allow him to wear them until he's ready.
However if he's not potty training by age 4 and 1/2 then you may need to force the issue because to go to Kindergarten he will have to be potty trained.
That is unless you decide to home school your child.
Some kids don't potty train until 4 and even near 5 years old.
My neighbors son didn't potty train until he was 6 and he was normal.
He just put up a fight about the toilet so his parents just gave up and let him decide when he wanted to use the toilet.