Why would she cheat on love of her life?

[Rosewaitcarpark]

Looking for opinions please. Recently found out my SIL cheated on her partner who she's been living with for quite a long time. She went on a few 'dates' with this other man, had sex a few times, then finished it. But she's always claimed that her partner is the love of her life. She regularly sings his praises. Talks about how gorgeous he is. She even left her husband for her current partner.
Her partner doesn't know about her cheating, but basically pretty much her entire family do. What I want to know is, is she lying about him being the love of her life, is she deluding herself?
Not even sure why she went with this OM.

You can love more than one person at once and desire other people whilst being in love with one person. No delusion needed. DP is the love of my life, but we have an open relationship (difference between me and your SIL, is that DP and I agreed it and we both know about it!)

Though if the entire extended family and presumably most of their friends are in the know and she isn’t very discrete in her conversations then frankly, I wouldn’t be so sure her partner doesn’t know. Perhaps he’s happy to turn a blind eye.

I think some people are more in love with the idea of being in love.

I knew a woman who was always going on about how great her partner is and how he was the one. Then she dumped him for someone else and she went on about what a loser her Ex was and how she couldn't stand him. She was a drama queen and nothing was ever done by half.

He definitely doesn't know because my MIL intervened once when I went to say something in front of him about SIL's dates with this OM (because I had thought they'd dated before her relationship started with her partner).

Also, when I raised it with my DH, he was very keen to change the subject, after saying that he thought his sister had gone on dates with this OM while she was on a break with her partner.

What does love of your life even mean? Presumably just the person you've loved most out of all the people you've loved so far. Not necessarily someone you love enough not to cheat on, if you're that way inclined.

Should I try to find a way to let him know?

@Rosewaitcarpark

Should I try to find a way to let him know?

Stay well out of it.

Infidelity seems to be the norm these days, for both sexes.

"he even left her husband for her current partner." tells you all you need to know really. there is a saying...when a man marries his mistress it leaves a opening.

@Rosewaitcarpark

Should I try to find a way to let him know?

Yes, personally I would.

Infidelity robs someone of their personal agency.

There is a growing belief it’s a form of abuse. It certainly harms the victim on all levels sexual, physical, mental snd emotional.

Even if you did it anonymously, I’d do it.

Should I try to find a way to let him know? - oersonally I think you should. Unless he knows about it he's living a life on false pretences. He should have the opportunity to decide what to do, whether to stay with her or whether to leave and maybe find someone who turly values him in the future.

The poor man, everyone knowing but him.

Personally, that should say.

Under no circumstances would I let him know. Unless you know a person in these circumstances extremely well, its incredibly arrogant to think you know what they would or wouldn't want to know, and to take it upon yourself to intervene in their relationship. For all you know he could be aware already or may prefer not to know. I would say he would almost certainly prefer not to be told by someone who wasn't close to him, and have his works rocked either anonymously or by a conversation with his partners sister in law. If 'everyone' knows, I'm sure this will include people close to him who are better placed to know what is in his interests.

Some people are just sexually incontinent and like the attention from new people. I don't think there's too much more to it than that, it's not some great mystery

Tell the poor man.