It will fall as long as bitcoin cash has a strong hold in the market. Currently bitcoincash is at 20% of the price of bitcoin. Since they were forked, therefore the total value is what actually reflects the value of a bitcoin. If BCH goes up, then btc will go down.
Yes I think big whales doing some large-scale manipulations. But it not good for original bitcoin I think.
Also I read that mining bitcoin cash is more profitable now than mining bitcoin...
Anyway, long-term holding is the best ever thing, at least for me.