In this day and age, most of us have friends of the opposite sex, whether they are co-workers, casual acquaintances or close confidantes. The question is: how close is too close when you're in a romantic relationship with someone else? Here are some signs that your so-called friendship may be entering the not-so-gray area of emotional infidelity:

1. You dress up for him. When you buy new clothes or change your hairstyle and wonder what he'll think (instead of how your partner will react) that's a danger sign. We all consider our audience when we're getting ready to go out, but doing so with a particular other in mind — not your significant other — suggests there's something more here than meets the eye. 

2. You lie to your significant other about seeing him. Perhaps you fail to mention an innocent coffee you had with him. You consider it just a small omission, not to be confused with a real lie, when you don't share it with your significant other. Maybe you even tell yourself you just forgot. If this is the case, you must ask yourself what you're hiding from your partner and why. 

3. You do special things for him that you don't do for others. You give him that cute card that perfectly captures how you feel about your friendship, or the little knickknack from your last trip which you imagine him placing on his desk. It seems innocent enough, but they are little reminders of you and invitations to reciprocate. What are your true intentions about this relationship and this person? 

4. You're spending more and more time away from home and/or your significant other.Late nights at the office are starting to add up. Long lunches are becoming routine. When you really think about it, you can see you're trying to increase your opportunity to spend time with him at the expense of the time you spend with your significant other. What is all this time with him really about? 

5. Your electronic communications are increasingly devoted to your non-significant other. You can't wait to surreptitiously check your phone to see the latest text from him. You're up in the middle of the night on Facebook. When the balance of who you communicate with tips away from your significant other toward someone else, it's a sure sign of trouble in both relationships. 

6. You laugh more with him. You "always" have more fun with him than with your partner. You like being with him. In fact, you prefer it. 

7. You think about him all the time. Your daydreams include this person almost to the exclusion of your partner. You muse about what would it be like to be with him all the time. 

8. You compare him to your partner. Comparing is a judgment, and judgments leave us feeling either really good or really bad. You think of him and you really feel good, and then you think of your partner and you feel bad in some way. 

9. You anticipate your next encounter. You are checking your email, phone or Facebook hoping he has contacted you. You feel excited and you are hoping he has contacted you. 

10. You feel understood by him, unlike by your partner. A really big red flag is when your thoughts wander towards "he really gets me. He knows exactly how I feel." Then you think of your partner and how he doesn't get you and he's a loser when it comes to your feelings. 

11. You tell others, "we are just friends." A big sign that you are more than friends is when others bring it to your attention what they are seeing. Don't ignore what others are saying. If you are defending your relationship with him with your friends, that's an issue to look at.

12. You feel uncomfortable when your partner says something about him. Many times these relationships are made at work and your partner does know about the "other" because of project work together. Pay attention if you feel uncomfortable when your partner (or spouse) comments about your work partner. It's important to explore your own conscience and be truthful to yourself about the relationship. 

13. You tell him things about yourself that you haven't told your partner. As a relationship develops, so does the depth of the feelings. One way to go deeper in a relationship is to tell things about yourself that you have not even told your partner. It's important to ask yourself, "why haven't I told my partner this?" 

14. You tell "little white lies" to your partner. There are "little white lies" because there's nothing going on and you don't want to upset your partner needlessly. Search your conscience and be honest with yourself about your motives. If there's nothing going on, then telling your partner should not be a problem.

15. You find it difficult to concentrate when he's around. This is an ordinary part of human sexual arousal. When you are aroused, your mind is absorbed by erotic cues. Other things become, well, less important. You lose track of time when you're with him. When the two of you are alone, you don't want to be interrupted. Nothing else seems truly worth the fuss. 

16. You show off for him. You smile more brightly. Your voice is more musical, more husky, more inviting. This is an ordinary part of the human mating dance. If you catch yourself doing it, that's okay, but be careful. You may want to sit out the next dance, until your capacity for rational thought fully returns. 

17. Your emotions seem more powerful and intense. Your mood can swing wildly, depending on whether you're getting positive signals from him or not. It's normal during courtship for your emotional controls not to work so well. Your job is to know that feeling a little out of control is a natural part of the early mating process. Time to take a deep breath before things get any more out of hand.

18. You feel more alive. This is one of the most dangerous elements of emotional attraction. The intensification of feeling and sensation that accompanies new love can be a powerful turn-on. Want advice? Try this: don't fight the feeling, but don't nurture it either. Just enjoy it as a pleasant reminder that you're still alive. Chances are you'll see the feeling fade over time. That's the good news and the bad news too.