You say he doesn't know how to respond to you and it struck me that I didn't know what you mean. Perhaps you aren't being clear enough in stating what you want in terms of response. Many women expect men to read their minds. This leads to vaguely communicated ideas, thoughts, feelings, and wishes and outrage when they don't get it.
No matter how much he loves you, he isn't a mind reader. Saying that he completes your sentences and vice versa only reinforces the illusion that you can and or should read each others minds. If you want to keep the relationship fresh, stop mind reading and start talking to each other in an open hearted way.
Stop completing each others sentences and ask open ended questions instead. Invite each other to talk about your deepest thoughts, feelings, fantasies, wishes, and so on. Talk about how you would like him to respond to you and be specific. You have said that there isn't any wow any longer. Instead of speaking in the negative, describe what wow means for you.
Be specific and communicate your ideas. For example, you might say, 'I would feel swept off my feet and romanced if you take me on a surprise outing once a week.' If you stop assuming and start talking about your thoughts, feelings, and wishes, you will be amazed at how fresh the relationship becomes.
Stagnation comes from lack of true emotional communication. Feelings are ever changing and always a surprise.