how do i treat my parents better?

sorry for the possibly long text.

for the past years i've noticed that i've been extremely bad faith towards my parents. i want to stop this. they're not the best and sometimes i do have bad feelings about them but i usually get over it. now it's gotten to the point where i can't stand to be in the same room as them.

i think it all started two years ago when they missed out my college graduation because they had a trip (to be fair they asked me if they should cancel it and i said they should still go because the trip was expensive). also with how they're treating my older sibling since they left our family a year ago. idek all of this happened for some time now so i thought i would have gotten over it at some point but i guess i haven't. i want to have a better relationship with my parents, or at least stop having negative feelings about them. they're the reason i have the life i have now. i want to be better to them. does anyone have any advice? thanks in advance.