Let’s face it, this is pretty awkward. You’re the same age as my partner and look like you should be going out with him instead of my dad. I sometimes wonder what people make of this curious foursome when we go out. What do they think the connections are? Father, daughter, son and his wife? Dad with three kids? I find it excruciating.

I’m not sure I’ll ever understand why an attractive, successful and smart woman in her 30s is going out with my slightly dumpy, definitely not-as-funny-as-he-thinks-he-is dad? Are you into older men? Was it that he was married? Or did you just get on really well?

Is it true that nothing happened between you while he was married to my wonderful mum? Did you really just get back in touch randomly after my parents divorced? That’s what he says, but I don’t buy it. I think he knows I would never look at him in the same way again if he admitted he had an affair.

I do desperately want to know how it happened. Memories from my teenage years take on new meaning: seeing texts from you on my dad’s phone; a friend spotting the two of you at a restaurant and him being startled; the “business trips” abroad. Not enough to know for certain, but apparently enough for my mum to ask you about it several times. I have to accept I might never know the truth, and so I have to pretend this is all normal and came about without a single wrong move.

I feel so torn in the way I should behave with you. In honour of my mum I should hate you a bit. But, out of loyalty to my dad, I also refuse to engage in family gossip about his midlife crisis. Sometimes, fleetingly, I feel proud he’s finally living the life he wants.

I get worried his new life with you is erasing his life with us, though; as if he’s trying to do it all over again. He’s even open to the idea of having more kids. He says he thinks he could do it a bit better this time, which makes me feel like a trial run.

Sometimes the way he speaks to you reminds me of how he spoke to my mum towards the end, and the way I sometimes hear myself talking to my partner when I’m annoyed – short, patronising and mean. It makes my skin crawl. I don’t think you’ll last, but I think he’s determined to stay with you to prove to everyone that you are truly compatible. Good luck with that.

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