And, here are my comments. Much of my reactions will have to do with evaluating a "new friendship" where many of the below dynamics are operating versus a seasoned friendship where trust has nurtured a deep emotional bonding which is not a threat to the marital trust but supports it. At the risk of being misunderstood--(I do not under any circumstances support a secretive, double-life, kind of inappropriate relationship) I venture some thoughts.
1. You think or say, "We're just friends."
This is used as a denial of inappropriate bonding is true. But this should not mean that all deep cross-sex friendships are emotional affairs.
2. You daydream about him or her.
Do you daydream about your spouse?
I don't think daydreaming about your cross-sex friend is necessarily a symptom of an emotional "affair." It can be, but it doesn't have to be. Pleasant, happy, thoughts about your friend may speak of emotional depth but not inappropriate depth; it may not violate any marital trust or vows. Good Christian wives who were faithful to their husbands and loved their husbands in the 1800's also had deep friendships with other women where they daydreamed about their friends. Daydreaming is not the same thing as lusting. I fear we may be urging the thought/dream police out here rather than encouraging healthy love and sexuality.
Now, if all you are doing is daydreaming about him or her, its time to discipline the mind--and maybe the relationship.
3. You look forward to seeing him or her.
Again, this is not so black and white. With sexual energy and deep fondness, you should look forward to seeing him or her. This is more problematic when you looking forward to seeing your friend more than you do your spouse. Do you delight in your spouse? Do you look forward to their phone calls? Do you look forward to your spouse's affection? Then, don't worry about looking forward to your friend if you have a deep friendship.
4. You want to tell them news first.
I would say this this was a pattern it would be problematic--if you want to share the news first.
5. You share intimate emotions.
This has to be taken into consideration with other dynamics. Obviously, I am going to say you want to share intimate emotions with your best friend--same sex or cross-sex. Sharing intimate emotions doesn't have to be a zero sum game--it does have to honor the marriage.
6. You share intimate problems.
This again is not a slam dunk when it comes to cross-sex friendships. If trust is built and there is maturity present, this doesn't have be a symptom for "emotional affair." A more nuanced observation would be if the friendship is pretty new and you find yourself discussing marital problems that, I would say is problematic. But once you get into a seasoned friendship, solid trust may be secure grounding for sharing intimate problems.
7. You believe he or she understands you more than your spouse.
Again, an important nuance here is the newness of the friendship or friendship intensity (you may have "known"this friend for years but suddenly there is intensity--that could be a "new" dynamic). However, if you get know someone real deep--hey, you know what, it is human, we all have certain blinders and our friends may "understand" friends at some points better than our spouse. However, overall (and please hear me on that--I don't want to be misunderstood) our spouse should always know us better than our friends.
8. You keep secrets and cover up.
I am on record as saying there is a certain depth in friendship that bears the fruit of secrecy. I hestiate to say that, lest I be misunderstood. But there is a mutual trust between husband and wife that may extend to the spouse's relationships where there is confidentiality may be the fruit of the friendship. This doesn't have anything to do with living a "secret" double life with your friend. Notwhatsoever. Living a double life as "just friends" is a deceptive dynamic.
9. You give gifts.
This not so black and white. Friends may share gifts with each other.
10. You spend more time alone.
No so black and white. This perhaps is something to watch for in a new friendship but there is nothing inherently wrong with a mature dyadic friendship and aloneness.
These flags may indeed point to unhealthy and inappropriate dynamics between friends. But we shouldn't take some of these as black-and-white signals that an inappropriate emotions are engaged.