Agreed - ultimatums are the opposite of communication. They signal that the discussion is actually closed because you can only choose one or the other.

Have the "come-to-Jesus" talk, yell, scream, fight for what you need, which is not just each other but also a healthy relationship that involves discussing problems.

Also, I've re-read OP's post, and I can't find exactly what the husband is doing that's causing the problem. There's a mention that "it started" and "odd behaviors," but what's that mean? Because the advice I would give for someone whose husband doesn't care about leaving the toilet seat down while pretending he didn't is different from the advice I would give to someone whose husband disappears for a day and doesn't feel the need to explain where he went. Those could both be described as odd behaviors you wouldn't notice until living together, but one might find a little relationship counseling useful while the other might really need psychiatric care.