Do you have a small hospital tank set up that you can put him in? If so, I would keep the lights off and not feed the first day and feed very sparingly the second day. Cleanup any uneaten food after 10 minutes or so.
He might be stressed because of the bullying. Once we find out that it's not any disease, I would get 6-7 more Tiger Barbs if these are your only 2.
I can't be sure of any disease based upon the given info tho. Does he have ragged fins or any visible signs of anything?
What size tank, what all is in there, how long has it been set up, what are your ammonia-nitrites and nitrates and how often do you change water/gravel clean and how much?