Most people generally aren't aware of the warning signs, he probably just assumed she was acting weird solely from depression and stress

My mom's boyfriend went through a temporary psychosis episode last winter, and for the first month or so we genuinely had no idea; we just assumed he was extra quiet/ solemn and sometimes a little grumpy. It wasn't until we pressed on some of his behaviors that it escalated to aggression and yelling at everyone, accusing us of poisoning him and messing with his vision, accusing my mom of being an undercover agent, the dog of having cameras in her eyes, then trying to run away with his passport, etc. All of these irrational things completely out of touch from his usual self seemed to come out of nowhere. (We called a crisis hotline and got him admitted to a psych ward, which I think ultimately saved his life before it was too late)

ANYONE of any age can experience psychosis for the first time (particularly from extreme stress, trauma, social isolation, and/or sleep deprivation); and when you enter that state you often distrust everyone around you, and so you may hide what's on your mind. Or you may phase in and out of your psychosis, experience memory lapses of many prior mental delusions, and are trying your hardest to appear normal to others, especially if you feel obligated to remain stoic/ strong for others. And like every mental condition, there's no universal presentation of it