The writing is pretty bad, and it's more than just the name flip-flopping back and forth.
If they were actually husband and wives and were "doing it" last night, then why the hell was the MC sleeping on the floor when the maid came in? It doesn't register in her mind as being remotely suspicious?
Also, the MC learned something important about Lilian last night, and somehow totally forgot to pass on that crucial piece of information to Isabella? Seriously?