you can still invest on etherium even though you have already invested on bitcoin because etherium is also a good coin with lots of potential and will probably increase more as the time goes by. investing in both is a good idea rather than foccusing on one , not unless you are already contented on what you earn from bitcoins.

now in the case of interest in cryptocurrencies. i guess people wont easily loose interest on it because cryptos is still new yet and it will still developed just like what you said. it is now too early to see the results .

 Some may lose their interest, some may not. The reason why others may lose their interest in bitcoin is if they suffer to losses and he/she can't get it back.
Some are not, because they still look for the good consequences or return of bitcoin someday.

Yes, people tend to change easily and it will take time to start rebuilding the trust if people on Bitcoin again and again. Even as at now when it is on a decline, a lot are selling off, while real investors are taking the opportunity to buy more. Hope deferred makes the heart weary, like waiting for a rise and it is now telling on their patience.

people are losing interest in bitcoin because they see social media scams bitcoin so they are afraid to invest.

First of all the end of bitcoin is never possible because from the date of its invention and till now, BTC has made its millions of users and millions of people are investing into BTC, so the end of bitcoin is impossible but if the worst thing happens and the bitcoin will ever die then I will use etherum to invest my money because it is second most popular cryptocurrency after BTC and it's valuation is also quite good.

I don't think people would lose interest in crypto currencies ,
First why would they lose interest in it if they are earning a profit from it?
I don't see a point in there,Because people tend to be more connected to something that is giving them profit .

Interest is a just for matter of time and people will switch to another coin. But once you know that a particular coin has good future and also have utility in everyday life, then one will hold that coin longer and keep its interest alive.

if bitcoin die, it will effect a lot on other crypto  as well.People will lose interest to invest on crypto which eventually make crypto a poor industry.But I don't think that bitcoin will die.If so then no other crypto will take the bitcoin place.

maybe someday, because bitcoin prices tend to be unstable. sometimes up and down. but i do not know when !!

I don't think Bitcoin is going anywhere. I do think that we have lost some potential investors for the short term because they were burned during the last $BTC bull run.