As a few people have said, if he was alone (or just with a mate,) he would have answered quicker and been more re-assuring.
Or maybe he just didn't realise he was on trial by Mumsnet and hadn't read the approved "Correct Response Guidance For Men".
Or maybe he doesn't have a guilty conscience and so felt no reason to do anything.
Or maybe he felt like shit, hoped he'd be home early, was a little over optimistic and fell back to sleep. Or was just procrastinating a bit, having a chat and drinking coffee. Does it really matter?
He was with another woman. Anyone who denies it is deluded.
Unless you were the 'other woman' he was with, you simply cannot state this with any certainty, or credibility.
I'm sorry but if it was me I'd be kicking him out.
Or you could, you know, just have a conversation...
Personally, I don't think going out 5 or 6 times without his wife is a great crime. I would go out more frequently than that without my partner and would be happy with the same. I'd probably prefer he didn't get outrageously drunk every time, but that's for health reasons rather than any 'fear' or 'outrage'. I wouldn't stand for being policed. I'm an adult.
I know from past experience that your partner/husband not going out without you is no guarantee that they won't cheat on you. If they want to, they will find a way. Why the need to keep someone on such a short leash?