Called the collateral ligaments, they keep the knee from moving sideways. The other two are within the knee, dead center, crossing each other as they rise from the middle of the tibia below to fasten to the middle of the femur above. Bettina's face falls. You mean it's torn. Well, it's kind of a moot point as to what's wrong.
Ligaments have some elasticity.
It won't go back. I think that's what's happened. Your ligament is longer than it was two weeks ago. And because it's too long, your knee is less stable than it was. In a way, it doesn't matter why.