How far ahead should you think when leaving a relationship starting a new relationship?

My marriage has been bad for years... The entire time 20 years. We hit rock bottom two years ago and sleeping separately mostly since. I met this girl online s year ago, I don't think it's long term but I like her. To separate I'd need to sell two properties. Give the cash to my wife and she gets her own place. I would keep the family home.

Meanwhile I don't see the new relationship lasting, should I separate and start new life.
How far ahead should you think when leaving a relationship starting a new relationship?
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