It's going to be tough for them to convince anyone they "borrowed" the truck since on the surface it appeared they are the thieves. The true thief would have to come forward and incriminate himself which he may not wish to do. Each defendant should have a lawyer because there may be a way to suppress the search.
What can happen to them? Well, the worst-case scenario is that they face significant prison time, as in over five years. Without knowing your boyfriend's criminal history, if any, or the criminal history of his friend, it is hard to say. Why did they borrow the truck? Where were they going? Who was the friend they "borrowed" it from and would a reasonable person have known the vehicle was stolen? What is the criminal history of the borrower and how long did your boyfriend know him? Well enough to know that is he could not have owned such a truck? How much drugs were found and where in the car? As one of the prior posters said, in drug sales cases wherein the drugs are found after a traffic stop, a motion to suppress evidence is something to look into. What was the reason for the traffic stop? Lots of questions to answer before I or anyone else can give you a clearer answer.