My friend is married to her soulmate and they have a perfect marriage, she is SAHM and he is a high earner, and they are settled on having just one DC, who is 5 now. Or so she thought... They have a "best couple " that they go on holidays together, celebrate all the major events together and generally are very close to. The lady in the couple is also a high earner and she works for the same company as my friend's husband. So the "best couple " lady has just had her 3rd baby (roughly 3 months ago), same sex as my friend's DC (yep, that's where its going) and my friend has obviously been delighted, supportive and generally very involved... and so has her DH. My friend is driving herself mad because the new baby has an uncanny resemblance to her DC and her DH. She has been digging a little in her DH phone and did find flirty messages and very caring messages between those 2, but nothing more.... and on top of that her DH is getting a massive severance from his job, so he literally never has to work again.
She is scared to ask questions, and I am advising her to seek legal advice, just in case she might find out that not only her DH has been cheating on her, but also is responsible for another child out there.
I think that forewarned is forearmed.