My ex told me he just didn’t hear our two babies when they woke at night. Too tired, just didn’t hear them. I believed him.
When the younger kid was 3, the ex told me he’d lied! Smiled about it. ‘I knew you’d get up! Of course I heard every time’.
Divorced him 6 months later. Like you, it stuck in my craw.
Not me, but I had a situation where I was looking after a small bundle... If that bundle stopped it's snuffling breathing throughout the night I'd instantly be awake, watching the clock and listening intently for next snuffly breath... If it woke up and cried/made noise? Wouldn't even stir, drove me and partner nuts.