To assume this is an excuse for cheating on spouse

[untilgertie]

When someone has been cheating on their spouse and their explanation is, 'I must have been unhappy', would it be reasonable to assume that this is an excuse for their behaviour that either they've come up with or someone else has suggested to them to say?
Wouldn't they say, 'I was unhappy'?

Both are excuses.

I “must have been” is just even more crap of a one. Yeah you were SO unhappy you didn’t even notice it at the time 🤔

I agree that both are excuses for inexcusable behaviour. But saying 'I was unhappy' somehow conveys more of what they believe was the truth of their state of mind at the time. Stating, 'I must have been' sounds like something inexplicable has happened and they're searching round for reasons.
Or, someone has said to them 'you must have been unhappy', and they're regurgitating that.

If you’re unhappy then you should sort it out with your spouse and either work on it or divorce not sleep with someone else- it’s a rubbish excuse

I think they are trying to deny responsibility for their behaviour.