Yes your boss is liable for sexual harrasment and you are a victim of sexual harassment in the workplace regardless of your refusal to give in to perform the sexual favor.
Section 3 of Republic Act (RA) 7877 or the Anti-Sexual Harassment Act of 1995 provides:
“SECTION 3. Work, Education or Training -Related, Sexual Harassment Defined. – Work, education or training-related sexual harassment is committed by an employer, employee, manager, supervisor, agent of the employer, teacher, instructor, professor, coach, trainor or any other person who, having authority, influence or moral ascendancy over another in a work or training or education environment, demands, requests or otherwise requires any sexual favor from the other, regardless of whether the demand, request or requirement for submission is accepted by the object of said Act.
(a) In a work-related or employment environment, sexual harassment is committed when:
(1) The sexual favor is made as a condition in the hiring or in the employment, re-employment or continued employment of said individual, or in granting said individual favorable compensation, terms of conditions, promotions or privileges; or the refusal to grant the sexual favor results in limiting, segregating or classifying the employee which in any way would discriminate, deprive or diminish employment opportunities or otherwise adversely affect said employee;
Based on your short narration it evidently, it appears that you are suffering from discrimination as well as the diminution of your benefits subsequent to your refusal to go out on a date with your boss. Hence, your boss may be held under the Anti-Sexual Harassment Act.