Some people aren't really loyal to you. they are loyal to their need of you. once their need changes (like if they found someone else that would keep them from being lonely who I guess is better than you), so does their loyalty.
“A man without a vision is a man without a future. A man without a future will always return to his past. Women will also do the same if they don't build a future with their man, they will return to their past as well