If my boyfriend has hit his head hard enough to produce a large bump should he go to hospital?

Maybe. Signs a head injury need the er: any loss of consciousness confusion / difficult to arouse vomit more than once vision, hearing or speech problems weak / numb in part of body blood or fluid from ears, fluid dripping from nose check him after 1st hour of sleep & periodically thru that night to make sure he wakes up like he normally would wake up in the middle of the night. Ice the goosegg.
Bump. Ice to the bump is important. If he has a headache, change in vision or the bump is getting bigger, he should check it out.