What he can do and what he is obligated to do as a matter of law requires more careful thought. A B-2 visitors visa is to be used by those who 'do not' have immigrant intent for the purposes of the visit.
B-2 visa abusers can be denied entry, turned back, and have their visitors visas cancelled. Some, particularly those who get angry, may even be charged with Section 212(a)(6)(C)(i) immigration document fraud. This creates a permanent bar from admission without a Section 212(i) waiver approval. Some waiver petitions are not approved. Yes, this may happen to someone who is married to a U.S. Citizen as a matter of DHS discretion. Although a permanent bar is extreme, this is possible, even if a few may claim it is unlikely.
I strongly suggest that you schedule an appointment or teleconference with a candid and very experienced immigration attorney. Perhaps, there are more appropriate legal options based upon your situation.
This is general information, not more detailed legal advice. This does not create an attorney-client privilege.
Although it is possible to adjust under a B2 visa, there are other issues to be taken into consideration. B2 is a non dual intent visa. It might be a problem when you adjust. I will advise to go the safer route at this point and opt for a K3 visa. Therefore, you might want to make it safer for you. Do not forget to disclose that he is married to you.
Note: The above is provided for informational purpose only, one should not act or refrain to act just on the information provided. No attorney-client relationship is created unless a retainer is signed.