Give the first priority to your mental health please;
Later on look into the matter calmly...

It’s the height of love in which you’re involved but sorry, I suspect it one sided only as per the boy’s behavior towards your elders...

your mother should’ve been respected by your fiancé...as in the early days of an engagement/ relationship normally people act upon at their best, but he seems a bit short tempered, secondly your all maternal relatives do not have any good opinion regarding the boy and in a long term relationship it’ll create more complications...

So think and act upon wisely you'll attain to an acceptable conclusion Insha-Allah! :)