He was stab by a black when he was younger how can I get him to be comfortable around my best friend

Has he seen a therapist to help him deal with the after-effects of his trauma?

There isn't much you can do other than don't try to force him to interact with your friend. This is something he has to handle on his own with the help of a therapist at his own pace.

However, you might encourage him to talk to the friend on-line or through texting. Getting to know the person without being distracted by physical appearance. But once again, he needs professional help to work through his negative feelings and to feel safe again.

Let your boyfriend get comfortable at his own pace. You cannot
Force anyone to do something that they don't want or like. You can't also make someone do something that they don't want to do. Your boyfriend might feel you're manipulating him if he senses that you're doing things to make him get comfortable as soon as possible. Give him time.

You may have the best intentions but if he feels that way then he
Must have been traumatized by the incident in the past. He needs you to understand him and not judge him. Do you know if he has been diagnosed with
Having PTSD or something? Post-traumatic stress disorder can
Hinder your boyfriend's ability to move on if he has it.
If he has it, then you definitely should give him emotional
Support.

I always post - and Stellaw keeps repeating me - that you can't make anybody do anything. I think the more you force this issue the worse it will get.

I agree with "Cat" - he needs to speak to someone, not just because of your best friend but because it's a mixed race world in general and these feelings must be upsetting to him.

Will he talk to someone? Has he?