Ethereum is not going down on the USD pair. It is going down on the bitcoin pair and that was expected for every altcoin. This always happens when bitcoin goes parabolic. People always want more bitcoin than altcoins in the end of the day. Altcoins are a vehicle to get more bitcoin.
ETH will probably surpass $200 in a matter of hours - https://coinmarketcap.com/currencies/ethereum/ and I cannot understand why the second biggest crypto in the market will go down while others are beginning to feel the effects of bull run that is currently going on? Also, I think ETH has its own strengths as a crypto making it a top contender in crypto dominance.
Because it's not automatic, price movement depends on the traders and investors action, maybe at this time they love to trade other altcoins but we can never loss on our faith in ETH as like you said, it's the number 2 in the market, so it will certainly rise.
Yup! Too many people just expect pairs to rise when btc pumps. It's not a given: traders make the market move.