Most of the other answers here seem to place all the responsibility on you. This is a clear case of sexual harassment, which is illegal.
If your company has at least 15 employees, then your employer bears the responsibility for ensuring that your workplace is safe, including that there is no sexual harassment. See San Francisco's Sexual Harassment: Frequently Asked Questions. If your employer refuses to address this behavior, you have a very strong legal case.
The point and purpose of Title VII of the Civil Rights Act of 1964 is to eliminate the need to choose between your dignity and your job. Under that act, your employer is required to address sexual harassment... it's not up to you to stop it. If your employer refuses to do so, they are violating the law, which is meant to protect you from exactly this situation. You have legal rights. Your only responsibility is to exercise those rights.
If your company has less than 15 employees, and your employer refuses to address the harassment, then you should still consult with a lawyer. This kind of behavior may still be considered assault, and you may still have legal protections, but a lawyer would be better able to make that determination.
You should not fall prey to victim blaming. The other person is the aggressor here, and you should not be made to change your behavior or routines to accommodate his disgusting behavior.
Since you've updated your answer to indicate that your boss has, indeed, taken some initial action, keep in mind that the end goal here is to make the harassment stop.
Things can get a bit ugly, because it's unlikely that the aggressor will own up to the accusations and the friendship between him and your boss could make things complicated. If you get into any kind of back-and-forth, remember to stay focused on what you're asking for: that you want the harassment to stop.
Your goals should not include any kind of discipline for the aggressor, including dismissal or reassignment. Asking for or expecting those things could cloud the issue and bring your motives into question (unfortunately). Legally, your boss is only required to ensure that the harassment stops. You, likewise, should not be required to accept reassignment or severance. The goal is to make the harassment stop.