My boyfriends penis has what looks like a little tunnel type hole on the top of his shaft about halfway. nothing comes out of it. is it a problem?

Hard to say: But a "tunnel" should not be anywhere but the tip of the penis, as in the urethra. Some men have the urethra come out of an area besides the tip(so called hypo or hyperspadias). Even if this is the case, he should see his primary care doctor or a urologist for a formal evaluation. Best of luck.

Congenital Defect?: This is a very common thing in men, about one in 250 baby boys are born with a variant placement of the urethra. This is referred to as Hypospadias. Surgical repair is something necessary and is performed usually when babies are about 7 months old. Did you ask him about this? It could be an enlarged pore or a piercing site as well. Don't be afraid or embarrassed to ask him. Probably no problem.