The answer depends heavily on whether or not you want to end the relationship -- because, you're going to have to do one of the following:
1. Threaten to, and if necessary, fire your boyfriend and hire a new manager, if your boyfriend won't cooperate immediately.
2. Collect all of the financial records for the business from the various banking institutions and office files, and then hand them over to a CPA
for a "forensic accounting." And, if your boyfriend gets in the way, then you will once again, have to threaten to or actually terminate his employment. You could also, have a locksmith rekey the business so that your boyfriend cannot enter without your consent. Then, you would have to keep him out while you collect the records you need.
I realize that this may be extremely difficult for you, but the botXXXXX XXXXXne is that if your boyfriend won't turn over the records, then something is wrong, and whatever that something is, you need to find out, because it may involve some sort of fraudulent activity, which could mean that he may be misappropriating assets or cheating your customers/clients. And, that's in addition to potentially rowing you on board for a tax evasion prosecution by the IRS and possibly the state department of revenue, depending upon the nature of the business.
Ultimately, if your boyfriend refuses to cooperate, then you may need to get a domestic violence protective order from the court to keep him away from you and the child -- and then ask the court to formally order child support payable to you.
Hope this helps.