Leavenheath
From others' posts apparently the OP has been worried for months and in the summer was especially concerned because her husband would contact this relatively new woman friend on waking, communicate throughout the day and then during the evening at home.
They're colleagues and friends. They probably spend as much time together as OP and DH throughout the week. So of course they communicate throughout the day. And messaging in the morning and evening is hardly a hanging offence.
And it's important to remember that a fair amount of this is Chinese Whispers -- I'm going by your summary of other people's comments about comments on a thread that neither of us has read.
From the way in which this thread has been conducted, I wouldn't be at all surprised to learn that this boiled down to 'he has texted her once or twice before leaving for work' and 'occasionally texts in the evening'.
He was also buying the friend presents. The OP says he isn't in touch with any other friend that often, doesn't buy them presents and has never done this before.
Again, what sort of presents and how often? Is it unreasonable to buy a friend presents? If he were frittering away large sums of family money on red roses, chocolates and champagne I would understand the concern. But I am willing to bet cold hard cash that this is yet another mountain out of a molehill.
If anyone can prove me wrong, go ahead. I'm quite curious to know the details myself, but don't know where to look.
I'd be frankly astonished if any naysayers here would be unpeturbed by that changed behaviour in their own partners.
Again, it depends how dramatic the change was, which is unknown. But we do know, from this very thread, that OP's marriage is in good shape, sex life is normal (and he's described as 'keen'), and she herself says she does not feel that he has in any way 'checked out' of the marriage.