It's best to be upfront with her. Sit down and have a clear conversation about how you feel, what you need, and why. Listen to her too, listening is the key to good communication, which is the key to a good relationship.
You can say recently you are vey busy with a big important project and need some private life,usually she will get you. Also it is very important to tell her to cultivate some interests and let her know you are not the only thing in her life.
