Hi -
He is able to come again. They will "re-examine" him when he re-enters and decide whether to let him in again or not, and for what length of time to admit him (i.e. for the same amount of time as last time or for a different length of time.) As they let him in once they will probably let him in again. He must convince them that his stay will be temporary, that he will leave at the end of the time allotted (the fact that he did preiously speaks well for him), that he has a job, studies etc. to go back to in his home country, that he has means of support in Canada, and that he has a genuine reason to visit.
Good luck!
I imagine that if the boyfriend arrives at Canada's border many times, the border Guard will wonder how he could have strong ties (job, studies) back home. This question might not occur at the second entry, nor maybe the third, but at some point he'll be asked this question.