I am sorry to hear that your boyfriend is suffering. Sadly Crohn's disease is very aggressive and it is important that your boyfriend ascertains what is triggering off any violent responses as a result.
The bleeding may be a symptom but it should be taken seriously. Locating the source of the bleeding is important and it could be a tear in the lining or from inflammation of the colon. Common symptoms include;
Rectal bleeding, fever, weight loss, abdominal pain, diarrhea and loss of appetite.
If bleeding is severe, it can cause anemia. Iron supplements may be needed. This is another reason why your boyfriend should seek medical help. Once the location of the bleeding has been determined, he may need iron supplements and dietary advice to help ensure he absorbs all relevant nutrients.
Crohn's affect people differently but there will be periods of aggravation and also, periods of remission.
I attach a link on Crohn's disease and hope that it helps.