How to support a friendship you don’t approve of?

So, long story short my boyfriend has a friend who has treated him poorly for the last few years! His friend will make rude comments, and hurt my boyfriends feelings! I told my boyfriend to speak to his friend about how the stuff he says hurts him, so, he did! But! The friend hasn’t stopped making these comments and hurting my boyfriends feelings...

I would prefer if my boyfriend cut this friend off, however, that obviously isn’t my right.. my boyfriend states he wants to continue the friendship merely because the amount of time they have been friends, even if that means his friend hurts his feelings from time to time.

What should I do? I want to be more understanding & supportive of this friendship....