Say you (early 40s) had a partner (mid 40s) who you have been with for two years. You live together and have planned to do life together. You start to realise that your partner is not always truthful with you. First it's about small things and then it starts to get bigger. He starts hiding the fact that he likes to drink more than you think he does etc.
You have a stressful medical appointment approaching and you asked him in advance if can drive you and be there to support you. The day before he says he is going round to a friends house in the afternoon to play darts. He calls you blind drunk later that evening to say he is not coming home that night. You are upset because he knows about the medical appointment the next day, he knows you're anxious about it, and you think he should come home. He turns up at the appointment stinking of booze with bloodshot eyes and is not much company.
You ask him who he was hanging out with the previous night because your intuition is telling you something is off. He says simply, 'his friend and some of his friend's family'.
Fast forward a few months and you find a strange message on his phone from a young woman. The message only makes sense if there were previous messages visible. But there are not. You ask your partner about this and ask whether he deleted messages. He admits he did and that he did so to avoid conflict. He tells you the message was harmless. You leave it but you just have this nagging feeling. The last name of the woman is the same last name of his friend whose house he spent the night at.
A few months later it comes up again and he admits that his friend's 20 year old niece was present that night. He says that she had messaged to see whether he wanted to meet up.
After more questioning a few weeks later, it is revealed that he flirted with her that night, that they had exchanged numbers and that they had messaged with the intention to meet up. He then thinks better of it and tells her he has a partner (which means he didn't tell her he had a partner that night). He admits that he liked the attention and was flattered that someone much younger found him attractive. They remain social media friends.
All of this comes out in trickles over the course of a month or so. All of this happens at a time in your relationship when you are just back from a wonderful overseas holiday and are starting to talk about planning to have a baby. Everything seems blissful to you, but this is happening in the background. It is only months and months later after other cracks have started to appear that you find this out, in trickles.