More likely than not, your chimney actually has its own foundation that’s wholly separate from the rest of the home. Although this can be useful in giving the chimney enough support so it typically wouldn’t start sinking quickly, it can also be frustrating because that means it’s completely separate from your home, without the additional support necessary to keep it in one place.
Another possible cause is that the chimney’s foundation simply isn’t strong enough to support its weight, and it’s sinking into the ground. That can cause it to lean away from the rest of the home because one side will typically start to sink more quickly than the other side. This can cause the brick cracking that you’re noticing.
No matter which signs you’re noticing, it’s important to recognize that this is a real and serious problem. You don’t want your chimney to fall over entirely, after all. If you’re seeing that your chimney is starting to have a leaning problem, or you’re noticing a lot of cracked bricks around the ends of the chimney, it’s extremely important that you address it as soon as you can.