The bisexual duality can not be satisfied by the binarity of one partner, leaving a lot of space for unhappiness, uncertainty and confusion, in a state where certainly might have been exspected.

This is an extremely common and extremely silly take. Bi folk aren't any more or less "satisfied" in a relationship than mono folk are. People (bi or otherwise) betray their partnership commitments all the time, but for whatever reason bisexuality seems to get conflated with infidelity / general profligacy. It's an ugly and inaccurate stereotype.

Lack of communication being a problem - sure. But you're conflating a few things.

1. In modern terms, bisexuality and pansexuality are interchangeable, the terms have evolved over the years and most of the community rejects the old distinction.
2. "The bisexual duality cannot be satisfied by the binarity of one partner" is the stupidest thing ive ever heard. They are bi, meaning their attraction applies to both (or more) genders. They aren't in heat with an unquenchable lust for sex with multiple genders. Someone can have a preference for brunettes and redheads and marry a redhead and not be "unsatisfied". The problem with closeted gay people marrying into a straight relationship is that they are denying their own sexuality, and lying to themselves. Bisexual people are not lying to themselves. They are attracted to their spouse. There is no confusion.

Huh? I'm bi and have been happily married for 30 years

You mean like the sexuality of straight people can not be satisfied because there are other hotter people of the same sex as their spouse?