My boyfriend violated his probation by stealing. He is currently in jail, I just got the call from him. Could he possibly just get a longer probation period? Or will he for sure go to jail?

Peole get probation usually because it was a first offence. Probation is the chance to stay out of jail, do better. If you violate probation you are given whatever sentence you avoided by getting probation. So yes, he'll go to jail. They already gave him a chance, and he blew it. They won't give him a second chance.