hi, i have cable net connection in my first computer which i share with second computer i use nic card to interface between computers. I have allowed this second computer to control over internet connection so, both computers can connect and disconnect internet connection any time they wish
but the problem is that, i cant see gateway in my second computer though which i can connect and disconnect internet connection. though i am able to access internet.

so the operator can access internet on my second computer, but operator on first computer has to connect it. he cant connect and disconnect internet directly from second computer.
which was possible before though internet gateway.
please i seek help how to get that gateway on my second computer again

That is how a networked system like this will work. Buy a router so each pc will have its own ip address.