Yeah, we've also known about Maya's issues since pretty early on and had to get strung along even if I didn't want anything to do with it during the whole game, e.g. being forced to go to the Burke's.
I think he's very aware things will take a turn to worse before they get better, he's either afraid of facing said problems or is just riding along and waiting to see what happens, but I'm pretty sure the questions are constantly hanging around his head when he's with her. Same applies to Isabella, probably even more so in her case.
in my opinion the photographic contribution makes the situation worse....
in quick succession Bella asked MC to clarify the situation with Jill and end things with her, but afterwards she is so worried by her reaction that she considers stepping aside.
And with all that, they still haven't checked to see if the BR rules provide anything for their situation.
if this is the level of concern for the one big problem they've decided to deal with obviously the second problem makes them feel quite comfortable, ok, MC knows there's something in Bella's past, but he'll have the doubt about how her husband died or which alien race abducted him, he certainly doesn't feel any danger from this mystery
it's more complicated to make judgments about what Bella thinks since she might as well be completely mad.
the excuse of shyness, of confidentiality no longer applies, they are no longer a couple on first dates, Bella has potentially put her job, reputation and the only friendship she cared about at risk