I too got frustrated looking at the episode and was cursing Archana for this...However, after recaping the entire episode whatever they showed makes sense...Archana and Manav had decided to help Shravani from the start. Whenever Shravani doubted Archana, she promised that she is not going to stop her marriage with Manav and she will go after 3 months. So whatever they showed in the episode is actually correct. This doesn't mean ArMan won't be together.
Now since the serial is going to take a leap what I think would happen is that after today Shravani will not marry manav and she will go away giving her baby to Manav or something...Manav might try to find Archana to tell her this but she would have already left the town and won't meet for some years/months whatever. Then suddenly they will meet up somewhere and Manav will tell her what happened and he still wants Archana to get back to her and then they will be united...All will be good in the end and ArMan would be together forever.
So chill out and don't be upset guys....This pavitra rishta cannot break so easily...