Unfortunately, this sounds like a classic case of midlife crisis on his part. If he’s out partying regularly; chances are he’s going to find a new partner pretty soon. Seek legal advice ASAP. Protect your assets and interests. Don’t let him start spending your joint money on ‘tarts!’ Open a separate bank account. Realistically consider if you will need to move out of the family home in a divorce settlement situation. If so-where will you go/how will you fund bills etc?
Get busy. Get ****** off with him. Grieve later. Empower yourself by finding out your legal and financial rights. Talk with a psychologist if emotions become overwhelming.