Yes, you can challenge DHR in court. DHR is widely known for overstepping their authority, and people rarely challenge them simply because they don't realize they can. In fact, DHR does not have the authority to "order" you do to anything. In order for you to be under an order, the order has to come from a court. Not following DHR instructions could result in you being taken to court for a judge to review the situation and could result in a judge ordering you to do what DHR says, but you do have the right to challenge them in court. If this situation is an overreaction to your boyfriend merely exercising bad judgment on one occasion and if there are no substance abuse problems in your home, then you need to get DHR out of your life as soon as possible.
I would suggest that you go see a lawyer who handles family law cases as soon as possible to discuss your options. Also, I am aware of situations going on in your part of the state in which DHR has attempted to have people prosecuted for neglect or abuse over similarly minor issues that do not actually qualify as criminal offenses. Thus, you may need to go consult with a criminal defense attorney as well in anticipation of possible criminal charges. Their "investigation" is often just an attempt to shift the case to the district attorney's office, so that the costs of the case come out of the prosecutor's budget rather than the DHR budget.
Go see a lawyer who isn't afraid to stand up to "the system" and get some advice on protecting your legal rights.