why-didnt-lord-ram-try-to-prove-mother-sitas-purity-but-rather-chose-to-exile her? was Adharma ?
The exact answer why shree Rama sent Sita on exile in the forest and not again took her Agni Pariksha is given in Padma Purana – Volume 5- PATALAKHANDA - Chapter No. 57 -The Washerman's Former Birth . Page no. 1879 –Motilal _Banasirdass version. The whole chapter is fully dedicated just for answering this question.
According to Padma Purana once when Sita was young and still unmarried was playing in the grove of the garden heard the discussion of two parrots. about her and Shree Rama.
3-11 That pair, enjoying (each other's company), quickly flew in the
sky, settled on the lap of a mountain, and spoke (to each other): and
spoke (to each other): "On the earth, charming Rama will be the king.
His wife will be (a woman) by name Sita. The intelligent, powerful
king, vanquishing (his enemies), will rule (over eleven thousand
years. Blessed is that queen Janaki, and blessed the earth) along with
her for is he, named Rama, who having approached each other, will
gladly enjoy.
When the couple of parrots was conversing in this way, Sita understood that they are talking about her and realized that this is a divine couple. She then said to her friends: ''Slowly catch this charming pair of the birds." The friends just then went to the mountain, and caught the excellent pair of the birds. The friends just then went to the mountain, and caught the excellent pair of the birds. Then Sita asked them about what they were discussing. Who are you two where have you come from? Who is Rama, and who is
Sita? Wherefrom did you have the information about them!! ?
The pair of birds said:
19-26. There is a very great sage Valmiki who is the best among those who know dharma. That sage made his disciples sing the future
adventures of Rama. He, engrossed in the wellbeing of all beings,
everyday remembered its words. All those future adventures of Rama,
being sung repeatedly, were heard by both of us; they came to us (i.e.
were mastered by us) due to repetition. Listen to them. In the end we
shall tell who that Rama is and who that Janaki is and what will
happen to her with Rama of a playful nature. Glorious Visnu, good
stories about whom are sung by celestial women, will, having divided
himself into four, come up at the sacrifice performed by Rsyasrnga.
He, having a bow in his hand, will come along with Visvamitra and his
own brothers to Mithila. Then there seeing a bow difficult to be taken
(i.e. wielded) by other kings, he will break it, and will obtain the
very charming daughter of Janaka. O excellent one, we have heard that
with her he will rule over a large kingdom. O you of a beautiful body,
we who had flown there, heard this and other (things) about you, told
by those who lived there.
Then the pair of birds asked Sita to let them go where they are living.
Hearing these words, Janaki telling the couple of birds about the charming and enticing (story of) her birth, said to them: "I am that Janaki. the daughter of Janaka, whom you mentioned. I shall truly release you when that very charming Rama comes to me; not otherwise—
41-53 Hearing these words they trembled and were frightened. They were mutually (i.e. both) afraid; (and) said this to Janakt: "O good
lady, we are birds, living in forests and resorting to trees. We
wander everywhere. We would not get happiness (merely by staying) at
home. I am pregnant. Having gone to my place and having given birth to
sons (i.e. young ones) I shall come (back). I have told you the
truth."
(Though) thus addressed by the female parrot, Sita did not release her. Then her husband (i.e. the male parrot), eager,
and with his face hung down spoke to her: "Sita, release my wife. My charming wife would be (i.e. is) pregnant. Having performed her (i.e. after her) delivery I shall come to you, .Thus,, addressed, Sita said to male parrot "O you very intelligent one, you can gladly go. I shall keep this happy one, doing what is dear to me,' near me.
57-66. Though admonished with various words, she did not release her. The (parrot's) wife, who was angry, and miserable, then cursed
Janaka's daughter: "As you are separating me from my husband, in the
same way you will be, when pregnant, separated from Rama." When she,
the afflicted one, was repeatedly saying like this, her life departed
due to misery, full of the distress of her husband. For her who was
repeatedly remembering Rama and uttering (the name) Rama, a divine car
properly arrived. The female parrot became luminous when she had gone
to heaven. When she died, her husband, that lord of birds, was
extremely angry, and being distressed, fell into Gariga: ''In Rama's
city, full of people, I will be born as (a sjjdra so) that due to my
words she will be dejected, and extremely unhappy due to separation
(from her husband)." Saying so, he who was distressed, angry,
frightened and shaking due to separation from her, fell into the
water of Ganga graced with eddies. Due to his being angry, due to his
being distressed, and due to his having insulted SIta, he obtained
very (mean) sudrahood (as he was born as) a washerman named Krodhana.
That best bird (or best brahmana) who, doing ill to the great,
abandons his life through anger, obtains sudrahood after he dies. That
took place. Due to the words of the washerman she was censured and
separated. On account of the curse of the washerman, she was separated
(from Rama), and she went to the forest.
Conclusion – So from this story of Padama Purana ,we come to know
that Sita faced exile in the forest and separated from Shree Rama
while she was pregnant because of curse of divine Parrots. And just
because of the curse Lord Ram didn’t try to prove Mother Sita's
Purity again by Agini –Pariksha but rather exiled her. And after
all this was just LEELA of Lord Vishnu’s avatara shree Rama so it’s
not considered adharma cause we don’t fully understand divine
leelas.