Personally, I'd be happy to see us out of NATO and concentrating our somewhat meagre resources on defending this island. If the EU ends up with its own army, it can do the job of defending the EU. Russia only wants secure borders without any large army camped near them. If that's understood, there will be no problem with Russia.
We, however need to concentrate on our seaward borders with navy "coastguard" vessels and RAF maritime surveillance and both those functions need to be well set up.