I think that John and Katy obviously need each other in their lives and love each other very much. When it comes to having problems though, I do believe they have many problems that exist in their relationship. It seems that their main problem is boredom. They have been living their life the same way for a very long time, and John's way of escaping that routine is by going out wit his friends. Katy's way of dealing with John leaving is by getting angry with him. Instead of leaving the situation or getting angry, they need to talk about what's going on so they know how the other one feels.
You can tell there is a problem in the relationship, when John doesn't realize how much he truly cares about Katy, until she is gone. At that moment he says how he is going to change his ways and be a better husband. Yet, when Katy walks through the door, John's whole outlook on the situation changed. My thoughts are that John thinks it's a lot easier to say you're going to do something, than to actually do it. Yet, another problem can be that John doesn't even realize that him going out every night is hurting Katy.
In conclusion, I believe that there is no doubt love in this relationship, but the problem is a very big lack of communication. Once they learn how to openly talk about things, Katy will know why John goes out every night, and John will know why Katy gets mad when he goes out. In the end they might realize that they can go out together and try new experiences to give their life some diversity. Also, maybe they may need some time apart from each other to finally realize how important the other person is in their life. All in all, John and Katy definitely have some kinks to work out in their relationship.