How to avoid chicken getting too tender when cooking in a crock pot?
Funny you should ask about this as I have just been experimenting with tough old chickens.

Your chicken is falling apart because the connective tissues in the meat are being turned into gelatin.

Cooking meat in a wet environment at low temperatures causes the connective tissues (collagen) in the meat to dissolve into delicious gelatin and makes the meat more tender. Cooking at the lower temperatures means that the meat can cook for longer without over heating and maximize the gelatin conversion.

This is often a very desirable thing. Cheap, tough meat can be made delicious. Crockpots are designed to make this very easy.

Roasting in the oven is hot and dry. The meat cooks faster, not very much gelatin is converted and the meat holds together better (or is tough depending on the meat).

The solution is simple: Don't cook your chicken as long.

To taste done, your chicken needs to reach 140F. To be safe from bacteria, your chicken has to get up to 165F. (Actually, it can be safe at as low as 135F but you have to hold it at those temperatures longer to kill the bad bugs. This document has the whole time chart.)

You should use a thermometer to determine when the interior of your chicken is done and then stop cooking it. How long it will take to get your chicken to those temps will depend on your recipe, how much meat there is, what shape it is, and the properties of your crock pot.

Keep in mind that a crockpot is still wet cooking (braising) where an oven is usually dry. The outside of the chicken will never be as browned or crispy from a crockpot as from an oven.