When did Arjun and Purvi do IT?

I have got a question, everyone is saying something happened between Arjun-Purvi prior to their wedding;

I am totally forgetting that incident. But someone inform me that this happen when & how? After that I saw 30.08.2012 episode. After saw that episode I am totally confused & also stunned.

If Purvi is pregnant of Arjun's child after 6 months leap its only happen after chudi wearing ceremony. That night I not remember Purvi was crying coz some chawal women talking about purvi that she is marrying Arjun for money only. I think she cry only for missing  aai and aaghi. I also saw rain incident & after that. But very surprised that they were shown going towards small like house or cottage, but after that not thing shown. After we saw that Purvi coming home by auto not with Arjun & his car, when she enters home we saw purvi's face was hidden smile. Suddenly she saw Ovi standing near her house & ovi emotional blackmail Purvi that If purvi refused marry to Arjun & arranged married to her then she accept Archana is her mother & convince all family member to accept Archana.

But I am very surprised that after that incident we spent more than 3 moths. ARVI faces huge suffer when Purvi reject to marry Arjun & arranged Arjun married to Ovi. After that they missing each other very much & also we saw that much flashback between ARVI. But any time they can't remember or we can't saw that scene flashback. If really something happen that incident we also saw that flashback. But we can't anything.

So my question when they not remember anything that incident or we can't saw any flashback this incident, how all you are sure that Purvi was pregnant Arjun's child that incident?

I am totally forgetting that incident. But someone inform me that this happen when & how? After that I saw 30.08.2012 episode. After saw that episode I am totally confused & also stunned.