Most definitely this.
Also, anyone who thinks their life got ruined because their GF cheated on them needs to get over it.
Someone's life may encounter huge hurdles and indeed be detrimentally affected in significant ways if your long term partner (husband/wife, legal marriage) who they have many mutual assets with (and children) cheats on you. They have an excuse because that's just a massive pain. But I've met far too many guys whose Girlfriend of 4 months cheats on them and they moan and whine for 6 months about it.
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I don't see any justification of cheating, just explanations for why it happens. If people better understand it, then perhaps they can be more conscientious of it when making long term decisions about getting a life partner.
But we can always make the "OMG CHEATING IS SO DISGUSTING LET'S SHAME ANYONE WHO DOESN'T IMMEDIATELY ABHOR THE THOUGHT OF IT," response, rather than being rational human beings and taking a closer look at it.