I feel like I need to see where this could potentially go, but I'm also aware that my brother may not be ok with it.
My best friend has recently started dating my brother.
Just to encourage you to think about why this fills you with dread rather than it being a cause for celebration?
Ask yourself if they were describing the same relationship but with different people would you still be feeling anxious or using words like ‘disgust’?
If your feelings stem more from your problems with relationships and/or confidence, counselling may be of benefit If you have real concerns that won’t go away are you able to speak to them individually or together?
Frame this in a context of being happy for them but having some worries about how you feel.
We stayed up all night just talking the first night I was there.