There are many different types of meniscal tears but one of the most common is a "bucket" handle type tear, which is easily fixed arthroscopically. Unfortunately, the longer you wait to get it fixed, depending upon other factors (like activity level, if you are overweight, have other ortho problems like flat feet, hip problems, etc..) the worse things will get.
The risk of developing osteo-arthritis and other problems like a chunk breaking off and floating around in the joint (a dessicans) also becomes a factor if you don't get it fixed, with eventual arthroplasty possibly being required (knee replacement). You can use a good quality knee brace to help stabilize the knee in the short term, but then the muscles around the knee that provide stabilization without the brace tend to become weaker and introduce a host of other problems down the road, requiring the use of the brace all of the time, additional pains up and down the kinetic chain (feet, hips, back, etc..)
Plenty of folks get by for some time with minor tears, especially if they exercise and do knee strengthening work, etc.. to keep the knees normal stabilization mechanisms in check, but more serious tears will require medical intervention. This is due to the nature of fibrocartilage which has no, or very few blood vessels, lymphatic channels or nerve tissue to help it heal as other tissues in the body do so things heal very slowly, or sometimes not at all depending upon the tear type, and other factors.
Anyway, good luck with it - but if you can get it fixed please do so as the risk of arthritis and other related issues gets worse over time.