As mentioned before, love and relationships are very multifaced so having something from carnal desire isn't necessarily bad, especially since there are no two relationships alike. I think what's most important for a relationship to work is that you don't have one big "YES I DO" moment but decide wholeheartedly to love the other person each day anew and are willing to grow together but also as individuals. Note though that everyone in the relationship needs to do this, and sometimes you might also just ... stop loving someone, and that's okay too. It's perfectly ok to leave, it doesn't diminish the true feelings and relationship you had, it just happens to be over and you can find something new while still thinking fondly of the love you had. It is worse to hold onto something that actually is only an empty shell just out of convenience.
While I consider Pride & Prejudice as one of my favourite books because both characters actively try to change and be a better version of themselves period when the other points out their flaws, I still have to say that I don't think that many of the protagonists in Austen's novels actually marry completely out of love. I mean Lizzy regrets rejecting Mr Darcy after she saw his big estate. Sense & Sensibility also feels more like a convenient "I get along with him and he seems very loyal and does NOT impregnate young women to then ditch all the responsibilities." Their love is always very reasonable and intellectual, and if it is because the girls actually feel something passionate before they thought about it properly, it easily is condemmed (like Marianne and Lydia). The men get off the hook more easily, namely Darcy, probably because he doesn't appear very passionate to everyone else. Of course you need to read the novels with Austen's time in mind where eloping to Scottland was very scandalous and you wanted especially girls to behave "properly", but I don't think you can measure every relationship by Austen standards to determine whether it's "true love" and you "found The One"(which both are very stupid terms to begin with.)
I would say your view is very idealised and somewhat innocent/puristic and only works for a selected few relationships. Love being "sincere and truthful" can look very differently depending on the individual people in the relationship, and there most definitely isn't one right way. I just found that love is wayyy too much an emotion that you can rationalise it the way Austen's "good" female characters do. It's not rational. You can create a certain fondness or appreciation for someone on a rational basis because objectively you're a "good fit" but much like Darcy said, it oftentimes just goes against your better reasoning (and it can drive you crazy sometimes.) It's also not always mutual, or in the same intensity, sometimes the feelings are there but it just won't work out for other reasons.
Things might look great on paper and yet just won't work out in the real world.