I'm trying to hook up the ice maker in a new refrigerator. I didn't use a saddle valve. It didn't seem like a good idea. So I tee'd off an existing 5/8" line just downstream of a valve.

First problem was the valve which didn't completely shut the water off.
I cut about an inch of line away and put in it's place a T with two 5/8" connections in line and the quarter inch connection for the ice maker on the third side.

Things seemed to be going smoothly until I tightened up one of the 5/8" connections. It didn't seem like I was anywhere near overtightening it and then I heard a snap. The small collar that contacts the copper line partially split away from the body of the T connection. Now there is a very slow leak there, I'm concerned about tightening it further and I don't know how to fix it. The ferrule is likely fused to the pipe and as I cut the pipe midway along a linear run, I can't cut away the portion with the ferrule as it will no longer meet up with the T.

Is there a sensible way to fix this? or should I just come to terms with the fact that I'm in over my head and I should hire someone who knows what they're doing??