We don't live in a bubble. We spend time out in the world with other people and sometimes we make a connection with those other people. This is great, and a wonderful part of life. But it can become emotional infidelity when you are being more intimate with this new person than you are with your partner, even if it isn't sexual. It may be hard to draw the line sometimes but if you find that you are thinking of another person a lot, and not just in a casual way, it may be that you need to assess your own relationship.
It's very common that this type of emotional affair will eventually lead to a sexual relationship. That's one of the main reasons it needs to be nipped in the bud right away. There is no reason to beat yourself up about it just because you happened to meet someone and found that the two of you had an amazing attraction. What you do need to do, however, is to recognize that any type of infidelity is wrong and you need to put a stop to it before it goes any further.
The longer you allow yourself to spend time with this other person, the stronger the attraction will become and the harder it will be to resist temptation, or break things off. If you are sharing things with this new person about your relationship with your spouse, you've crossed a line. It's one thing to confide some things to your friends, but not someone you are attracted to. Doing so will only create bigger problems for you and create an 'unnatural' bond with the new person.
Your spouse is the person you should be sharing these issues with, not someone who you are having feelings for. That is a breach of the trust you and your partner share. By letting this other person in, more and more every time the two of you talk, you are distancing yourself from your partner. If you do that for too long, your main relationship will completely fall apart. And even though you may think that's what you want so you can have the new person, it rarely works out quite so neatly.
It's unbelievably easy to make more out of the time you spend with your new friend. After all, the two of you don't bicker, you don't have any issues with money or how to deal with the kids, etc. The day to day things that can drag us all down aren't shared by the two of you so of course things may seem wonderful. Just remember, they felt that way at first with your spouse too. It's inevitable. But don't confuse that with having found your soul mate. Your soul mate is more than likely the person waiting for you at home.
Emotional infidelity is very often the first step to a full fledged affair. It's very easy to have a connection with someone else, but when that connection seems to take on a life of it's own, you need to pull back before things get so far out of hand that you can't salvage the situation.