But I am not looking at this situation from Archana's perspective at all, I am looking at it totally as Purvi's plight.
Maybe in this day and age, it is acceptable to sleep with your intended a day before the marriage. I am not pointing fingers at the two for that. It does baffle my mind though that after all this, Purvi gave him up.
It must not have been easy for Purvi, the sanskars instilled in her must have rebelled against her instincts even in that hut, she did move away from Arjun, twice. If she finally did give in, excuses conceded to youth, proximity and love (there is a saying in Tamil, never put cotton and fire together, it will ignite), how could she give him up after that? A sanskari girl who gave herself up to him must have considered him her "all" to do that. Her mother's happiness took precedence over her feelings? Truly selfless or truly budhu.
As for Arjun, he initiated the moves in the hut, so how could he agree to marry Ovi at Purvi's bidding? He is not bound by the shackles of Archana's happiness so how was he, if he truly loved Purvi, able to contemplate marriage with Ovi? I don't give any credence to the reason that he wanted to prove his love to Purvi and hence agreed. He is more immature and foolish then than I ever gave him credit for :( he should have been man enough to have told Purvi that he could not go through this marriage, guided her in the right direction especially after what they had shared. Not only this, his undying love takes a leap and he proceeds to get Ovi pregnant? I understand the excuse "men will be men", etc., but this is Arjun, to whom the sun rises and sets on Purvi, in his wildest nightmares, he should not have been able to accept Purvi's demands of marriage with Ovi and/or have marital relations with Ovi. Even if his love was unrequited, a pavitra rishta, a love that was divine, sublime as theirs is touted to be, should have been able to withstand physical demands for six months, nay six years even.
To me, both Arjun and Purvi betrayed their love. They either knew not how to love deeply or blundered so badly that their trespass in the hut cannot be forgiven in the context of what transpired after.