Ms. Spencer has, as always, provided a thorough, sound and comprehensive answer to the question. The key in what she wrote, however, is that the advances were unwanted -- and clearly so.
It is sometimes the case that co-workers who have been in a relationship have difficulties and one employee, acting out of hurt and disappointment or anger, makes charges of sexual harassment to the employer. This almost always back-fires badly. You haven't provided any facts that suggest that this is the case, and if this is not the case in your situation, then just disregard this comment. But it is a common enough occurrence to bear a caution for those who find themselves in the circumstance of a co-worker relationship gone bad.
My responses to questions on Avvo are never intended as legal advice and must not be relied upon as legal advice. I give legal advice only in the course of an attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by individual consultation and execution of a written agreement for legal services.
By the way, can you possibly not realize this as an adult in the workplace?
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Yes, it is illegal sexual harassment, as long as these advances were unwanted. Don't put up with this and don't remain silent. Tell the co-worker in clear, specific terms you do not welcome the advances. Put that statement in writing and give it to the co-worker. Keep a copy for yourself. Tell human resources or management what happened and give HR/management a copy of the letter you gave your coworker. If the employer does not make it stop immediately, you should speak with an experienced plaintiffs employment attorney. To find a plaintiffs employment attorney in California, please go to the web site of the California Employment Lawyers Association (CELA). CELA is the largest and most influential bar association in the state for attorneys who represent working people. The web site is www.cela.org, and you can search for attorneys by location and practice area.
*** All legal actions have time limits, called statutes of limitation. If you miss the deadline for filing your claim, you will lose the opportunity to pursue your case. Please consult with an experienced employment attorney as soon as possible to better preserve your rights. *** Marilynn Mika Spencer provides information on Avvo as a service to the public, primarily when general information may be of assistance. Avvo is not an appropriate forum for an in-depth response or a detailed analysis. These comments are for information only and should not be considered legal advice. Legal advice must pertain to specific, detailed facts. No attorney-client relationship is created based on this information exchange. *** Marilynn Mika Spencer is licensed to practice law before all state and federal courts in California, and can appear before administrative agencies throughout the country. She is eligible to represent clients in other states on a pro hac vice basis. ***