You make a good analysis and give sound advice... yet I think your judgment on situationships is narrow-minded and limited. You seem to suffer from idealism, or “absolutism”: believing that only perfection or “having it all” (i.e. the absolute best, nothing less) is adequate.

> "However situationships are not a satisfying solution as it creates anxiety and uncertainty for one half of the couple."

Although not "perfect" solutions, these might be "good enough" and nourishing - as long as there's honesty and clear boundaries.

Since "the love of my life" for most people happens once in a blue moon (or never), between being solitary and sad and emotionally starved or having a situationship, the latter looks a much better proposition. I mean, I'd rather have a nice situationship than a unhappy marriage!

The truth is, most often than not we can't have everything we want: thus having "something good" should not be devalued or demonized.

> "The one who has the upper hand is selfish and immature."

This is one possibility, not the only one: s/he might also be experimenting, just enjoying him/herself, not ready for commitment yet, or just feeling "You're very important to me, but not THAT important or just right". There's nothing wrong in that: nobody's perfect, after all.