The phrase about "marrying an asset, not a liability" is literally about choosing a spouse.
Yes, and I wholeheartedly concur with it. So is it common or what?
Yes, but it has absolutely nothing to do with investment
Are you kidding? If you ask me,
that has everything to do with investment. And risk management. Divorces and divorce lawyers are not for kicks (and faint-hearted). It may turn out to be the best investment of your life ever as well as the most disastrous one
Regarding its use in investing or trading contexts, now I recall that I often met this expression in the commodities section of investing.com (in the crude oil part, more specifically). But as you were trying to search it on Google, now I'm seriously doubting that it is me who is to expect future misunderstandings. Maybe, you are not as knowledgeable as you think you are, both trading and English language wise? No need to get all defensive, just in case
Interesting. If it's so common, why does Google turn up nothing? It endlessly crawls the internet indexing things that people
actually say.

Maybe, you don't know how to search? In fact, Google can't search on closed forums which require registration just to read them, though I'm not sure if boards on investing.com are that closed (haven't been there for a while)
Kidding aside, searching the forum would suffice
Right, so literally
one post in four years.

The other posts you quoted specified
an investment/trade, which is exactly the point I just made
There's no reference to trade in these quotes, so don't twist their meaning please. They are all about not marrying an asset, investment, money, token (with the latter two being asset classes as well), the meaning being essentially the same, i.e. the one that I stick to here
As I said, tread carefully