I don't think loyalty in business is the same as it is with people you love. I think when your place of work no longer works for you, it's healthy to try and find another place of work, regardless of if the history you had with your company was great, when that changes you should look and see if you can get out on your terms. Very different from friendship and family.
You can be a loyal employee or business partner for 15 years, extremely loyal and if things change at your place of business it doesn't make you disloyal to move on... it just means you're willing to do what's best for yourself, which is healthy. I mean especially if you've warned the business that you've been working for, time and time again that they aren't living up to your expectations of them.