You might talk with one of the senior students and make your concerns known. Let the senior student address the issue with him. Yes, issues of the heart can be devastating but this does not bode well for the maturity of your sensei. Stepping on the mat under the influence is dangerous.
I agree, if you're senior you should speak to him, if not then ask one of the senior students to mention that it has been noticed and that the students are concerned about him.