What is when a guy says you keep me on my toes?

When a guy says "you keep me on my toes," it means that he feels challenged and motivated to improve himself because of your presence in his life. He likes to keep things exciting and constantly improve himself so he can keep up with you, as you are a source of inspiration and motivation for him. This phrase also implies that he values and respects your opinions, and is willing to make an effort to keep you interested. Overall, it is a positive indication that he is invested in your relationship and wants to maintain a healthy and fulfilling dynamic.