It is easy to develop a close relationship with a co-worker, especially if your work often throws you together, cautions clinical therapist Susan Healy in a “Huffington Post” article titled “Signs You've Crossed The Line With Your Work Spouse." You might not notice at first that your co-worker is hitting on you, but over time you realize the requests to eat lunch together, discussion about things outside of work, joking and casual touching are flirting. Limit the contact and conversations to work-related topics, ignore his overtures or ask him to stop as you remind him that you are married.

Your relationship with the co-worker could cross the line if you flirt back, encouraging him to continue, according to Nate C. Hindman in a “Huffington Post” article titled “Flirting Helps Women In The Workplace: Study.” Flirtatious behavior can damage your career and marriage, according to David Nour, a workplace expert and author of "Relationship Economics." Even playfully flirting with him when he hits on you could be misconstrued by co-workers and create problems for both of you in the workplace.

Set boundaries for appropriate behavior in the workplace, advises Segal. Don’t tell him things your spouse would find offensive or see as disloyal and don’t let him share similar things. Stay in public view whenever you are together and avoid sitting close enough for casual touching. Talk to your spouse about the situation so you don’t have secrets from him and nurture your marriage, Segal suggests.

If you cannot get the co-worker to stop hitting on you, take it up with your supervisor or human resources. Perhaps you need to have a different co-worker on the project or your co-worker needs a stern comment from your supervisor. If things don’t improve, talk to your human resources department about the company sexual harassment policy and how to file a claim, suggests Charlotte Jensen in the “Huffington Post” article “Sexual Harassment In The Workplace: 5 Things You Need To Know.” A sexual harassment investigation can sometimes create problems in the workplace, so use this as a final response.