Grammaretto, he may very well have forgotten his wife anyway - it's not at all uncommon in dementia for someone to cease to recognise their own spouse, or other close family for that matter - and it can happen quite quickly. With my own mother it happened in the space of a week.
One week her eyes would light up when she was me coming - the next,they were just blank - I was just a 'nice lady' who made her cups of tea, etc.
Of course it's very upsetting, though.
A friend's neighbour, who'd only had dementia for a year or two, became very upset and angry with 'that man!' in her house, and wanted him out! They'd been been married for over 40 years.