How we can go to the pari-nirvana if not by being a bodhisattva? I had noticed something that seemed to me a contradiction. I would be grateful if someone could resolve for me this contradiction .
To attain the state of pari-nirvana you need to liberate yourself from the lie of being a separate part of the universe, then the pari-nirvana through this prism seems to be an egoistic thing since you exit yourself from the samsara but you leave the other existences in  samsara.Which seem the epitome of egoism
But the bodhisattva return to the world for helping the other existences which seem more altruistic and by this way more close to pari-nirvana.
Therefore we get that going to pari-nirvana is in a certain sense a contradiction with being liberated from the lies ...
I hope I am being clear...
Thanks in advance !
What appears as a contradiction is the difference between Theravada and Mahayana paths. I cannot speak for the Theravada path since my study is Mahayana, but in our tradition, bodhicitta is necessary for enlightenment, eg: from the Diamond Sutra:

One who wants to give rise to the highest, most fulfilled, and
awakened mind must create this resolved attitude of mind: I must help
to lead all beings to the shore of awakening.

I have been taught that this is not a contradiction, but, rather, that Buddha gave many teachings, all tailored to the student. And that yes, it is possible to achieve nirvana, and become permanently liberated from samsara, the cycle of suffering, without bodhicitta. But that is not the path I am on. And whether or not it is possible to 'lead all lead all beings to the shore of awakening' is not the point. The point is having the intention to do so, and also, of including those you do not like.