The nut broke off and had a small red ring/gasket between these connectors. I’m an noob but can follow instructions. Please give suggestions. Thanks
Below there is a water valve 
which may be used as an alternative if the above (cupper?) pipe is inconvenient to use.
Not a lot of slack on that bend, gonna be a bitch and a half working on a new compression fitting and sealing it. Dog speed, OP
You’re not wrong on that. Might be easier to get some new pipe and couple of fittings to make whole new line.