i housed a male betta (crowntail) with 2 sunburst playties along with some other fish in a 55 gallon tank...at first he displayed the same behaviors (swimming in 1 spot...up and down the glass)...eventually (after about about 5 or so days) we noticed that he would attack any other fish that came near him; we disregarded it and figured the other fish would learn to keep their distance, we also kept an eye on him tho to make sure it didn't get worse. about 2 days later he would start chasing the playties to the middle of the tank attacking them. Bettas often confuse brightly colored fish (platyies, guppies, etc) that have longer/larger fins for other bettas and will begin to attack them...however, since you have a couple playties (and since they are a schooling fish) the betta may be feeling outnumbered and unsure of himself (b/c he may think the other playties are bettas who are gonan gang up on him)...thus unwilling to come out of his corner...this is mainly speculation, but i mean our little guy did the exact same thing at first...it took at little while, but then he was attacking everything that came near him or looked at him funny. also he did not readily accept food in the large tank. we set up an old 1gallon for him and put him in once we noticed this behavior and he has done WONDERFULLY since. he's big and fat and happy as ever! lol..good luck!