I felt the same way when I had surgery -- thinking sadly of all those muscle fibers melting away into skinny disuse.
Don't underestimate the trauma your body experiences in any surgery. You need to understand that modern medicine's ability to do major orthopedic repair arthroscopically in just a couple hours is indeed an amazing technical feat, but it is partly motivated by the Managed Care industry's financial considerations. Getting you in and out in 2-4 hours at a special surgical facility and not admitting you to a hospital with a room and an overnight stay helps them keep control of their costs. Unfortunately this has a psychological cost -- without a full hospital stay and its enforced bed rest, orthopedic patients tend to not take their own procedures as seriously as they should.Do NOTHING without consulting a PT or your surgeon.
The body is not a collection of individual isolated muscles, it is a complex supersystem made of equally complex subsystems. If you try to workout without medical guidance, you are nearly certain to develop maladaptive compensations in your technique that will be hard to undo later and will also increase your risk of injury down the line.
You are 31 years old. Go ahead and mentally give yourself a year off. There will be plenty of time to get yourself back into the kind of shape you want. Over your life span, missing 6-14 weeks of workouts now isn't going to make any difference in your ability to build and keep muscle. By far the best advice I could give you is to go to as many therapy sessions as your surgeon will prescribe and your income/insurance will cover, and be very conscientious about doing any "homework" exercises you're given. The more you devote your energy to getting through rehab, the faster you'll come back and the better your eventual outcome will be.