I was told from an MRI that I have a stage 3 ACL tear...there is no pain at all, do you need surgery for that?

I was playing football about 2 months ago, and my knee kind of wobbled and popped, it felt real weird so I stopped, and walked back home no problem. After a few hours my knee what huge and i couldn't really bend it well. I went to the doctor after a few days and he said it was a meniscus injury but said go to the doctor once i got out of school to have it checked out if the swelling was still there. A month later I go home knee still unstable and very swollen but no pain, i go to the doctor and i get an MRI. It took a while to come in and now the doctor tells me I have a stage 3 ACL tear, i find it hard to believe since ive played basketball on it ran on it and everythign for a while now, It pops a little and feels unstable but thats about the only time it hurts i feel about the same, but its been 2 months and its still swollen, does it need surgery and what exactly does "stage 3" mean?