From Rama and Sita's Leela point of view, this act of separation was done to invoke the mood of love while being separated, which is regarded as the strongest attraction between lovers. Mundane people abuse and curse Rama for such behaviour. In the process they only lower their consciousness to extreme darkness. Bhaktas on the other hand cry tears of joy and sing His Transcendental Glories and elevate themselves more and more towards the Brahmajyoti and into the Vaikuntha planets and even higher. If you think negatively of Rama for what He did to Sita, keep in mind that this was what Rama exactly wanted as a result of His gamble with His Honour. You're a part of His grand plan. After all, who can escape the Leela of Bhagwan Shri Rama?
God who came to earth in the form of Rama, who is supposed to be the source of inspiration for every human being doesn’t even think twice before putting himself under the sword of criticism, just for the love of his wife, for her Honour. Rama's Honour got a second blow when He (purposely) renounced His wife and sent Her to Valmiki's Ashram; an act which made people think about Sita again. In the end by putting a blemish on his persona of MARYADA PURUSHOTTAM, Rama raises Sita above all suspicions.
This can be accounted for -
The greatest love.
The greatest sacrifice.
Jai Shri Sita Ram.