I have an 100 year old house with CPVC plumbing. I am working on the tub. Water supply is a 1/2 inch cpvc pipe with a 3/4 threaded male piece on the end. Connected to that is an old valve. I have a new fixture. And a new valve that is for a 1/2 copper pipe in and a 3/8" pipe out to fixture. I want to use this new valve. How do I put this together. Or am I @#$% out of luck.

You are not out of @#$% luck. You can add a copper fitting to the CPVC and reduce to 1/2' copper. If any of this requires sweating you'd want to do that before screwing it on the CPVC. This is a common hardware store fitting.