Jessica, it's not all doom and gloom. I have had 4 knee surgeries, mainly for the exact same thing you have. My surgeon is very conservative and just trims away the minimum amount the meniscus he can to fix the new tear. Also like you, after my third surgery, I had a benign tumour grow in the synovial space (Doc thinks it was just caused by cell damage from the surgeries). Had that removed, alot of scar tissue and another tiny tear trim in my 4th surgery. My knee has been totally stable since then. It has been 4 yrs since that last surgery.
Make sure you keep all the muscles around the knee strong, that will help greatly with your rehab. Change your bike gearing and ride on compact cranks until the knee is stable and strong again. This took me 2 years and was the best thing I did. I am now back to full on racing, riding big gears, lots of hills, just generally back to normal. It has taken a long time, but can be done.
Best of luck to you, and I am sure you will have a great positive outcome from your surgery.