People change thoughout their lives. Sometimes for the better; other times for the worse. But change can be good. Everyone thrives on positive growth.
If you both found that there were negative changes taking place, it was a good thing you discussed it.
What are the issues he brings up? What "things" do you do that bother him? When you say his attitude and actions changed, what do you mean?
Is he still cheating? Does he have regret about cheating?
You both can make your marriage work but it will take patience and effort, especially because his discontent has been festering for two years.
If you both want to make this work, you can. And you may not "love him the same way," you may love him better. You CAN create a new, better, stronger and more vibrant marriage if you both face the fact that you both need growth and change. Start talking about what type of life and marriage/partnership you want. What do you hope for in a marriage partner? What sort of lifestyle do you want to lead?
Make lists and then exchange them. Grow together! Don't confuse stagnation for lack of love. The spark can return when you find there are new things to discover about each other.
Good luck and check back with us here!