I think it was parttimer79, who said that not being honest with the world would make things difficult years down the line.
Now I come from this as the wife of a man whose ex cheated on him, but never admitted it. She was adamant that they were just friends and someone she talked to occassionally for advice. What the ex didn't know was that my DH had found her inbox open on the PC and read all the sordid exchanges. So my DH confronted his ex and she lied and he divorced her. To this day she will swear blind nothing was going on. DH never called her out on why he knew she was lying for sake of their son but it did not sit well!
They divorced, and the settlement took ages, years in fact. The ex had to pretend that her lover was not living with her, the 3 nights a week rule. She needed the money from my ex, and I can see why she had 3 kids to support (2 from another relationship) but my DH refused to give in and would always maintain they had been in a relationship from the beginning and had been living together. DSS confirmed as much to him. So the ex had to keep her finances totally separate, pay for every bill herself for years. DH thought the new bloke was a sponger and dishonest for not committing to his ex.
DH was was living on a sofa bed and just wanted the settlement to be fair. The ex not being able to admit to the world what was plain to see, really ruined any chance of anything amicable. They were a couple and they continued to live a lie (FOR 3 YEARS!)
Before the settlement was finalised DH met and married me. We were honest from the start even if it did affect the settlement outcome. We did not want to lie or wait to start our life together. I can only imagine how awful it must have been for her. Waiting for the settlement to be over to finally come clean with the relationship. Then you have to witness your ex get married.
Finally a month before the 2nd hearing the ex confessed to the relationship and DH was geniunely happy for her that the new bloke was willing to settle down with her. The settlement was resolved and 2 months after that the ex got married.
Now DSS was young at the time of separation and had no clue. He is always asking his dad questions about his mum/dads relationship and his stepfather, like he was mums friend who moved in when you left home. DH feels rubbish in having to lie about everything, feels like he has been made to be the one who abandoned them. He also wants to ask about how we both met so we tell him. How on earth the ex answers these questions I have no idea. And of course there is always the chance that DSS will realise the truth one day, and how he reacts to that?
Hi OP if you are prepared to live a lie for sake of your ex then please think carefully about your kids. They grow up and ask questions, they are clever and come to conclusions.