I sensed even from your initial post's careful wording that suspicions of a deeper relationship between your partner and the designer were present. And if he's separated, and she's available, and they are 'extremely close', it's plausible – if not previously, or currently, then maybe eventually.
And given the work dimension, people tend to deny such things, and rationalize denial as being an entirely private and separate matter (even when it isn't). So while I regret feeding such suspicions, they're evident in your own word choices, and could explain the otherwise perplexing loyalty you report.
And given the work dimension, people tend to deny such things, and rationalize denial as being an entirely private and separate matter (even when it isn't). So while I regret feeding such suspicions, they're evident in your own word choices, and could explain the otherwise perplexing loyalty you report.