What strikes me about your post is when you say, "I knew that I couldn't be falling in love because I love my wife entirely." It is
possible to love your wife entirely AND to love someone else entirely. To me, loving someone entirely doesn't mean that they have all of my love, but that I love all of them. No one can really have all of someone's love because there is no shortage of love.
I think of it thusly: Love is at the center of all of us and what connects us to other human beings and other living things. It's the essence of who we are and fuels our passions, will to live, etc. All that happens when we feel love directed toward someone is that we let that person get close enough to us, or let ourselves get close enough to them, that they were able uncover the love that resides within us all the time. There is no end to that love. And sometimes someone new can tap into it and touch that love without a long ritual of getting closer -- for whatever reason, we sometimes just experience an instant heart connection with another and that connection allows them to touch the well of love we have. And that person may not even be in our life for very long but our feeling connected to them, and feeling our hearts expand, is undeniable.
Now the love we feel for a partner can grow deeper and stronger, as we become closer to that person, trust them more, know them very well, and find ourselves more "in tune" with each other. It's like we let them in further to that deep well of love that we have inside us, and it is comforting to have a special someone who has access to such a profound and inner part of us. But they don't consume ALL the love we have. There is always more love to give. We give it to friends, relatives, children, etc. We can love them entirely as well, but again that does not mean our love is used up entirely, just that we love them for all of who they are. The well of love is bottomless. So it is just a matter of whom we allow ourselves to get close enough to, or feel a connection to, when we love other people beside a special partner or spouse whom we have let in deeper than anyone else.
Now, all that being said, there is such a things as a crush or infatuation. That is usually a chemical bath we get dipped in! We are beings who have instincts and hormones and when the chemistry gets activated, we become aroused, euphoric, and dopey (on dopamine), beyond all reason. And it is beyond reason, because it's a very physical, chemical response, not a logical one. Unfortunately, it can be difficult to discern when it is just chemicals and when it is an instant heart connection, but I would suspect you can try by asking yourself whether it's a more deeply felt sense of oneness with a person rather than a heady physical turn-on. Maybe that will help sort it out, but it's best to not be too intellectual about it.
We can enjoy these crushes without necessarily acting upon them. Intimacy is not always sex, nor should it always lead to sex. There are all kinds of intimate situations we find ourselves with others -- a work environment, for example -- where we get closer to people and feel these heady feelings, but it would be inappropriate to take it further. For example, whenever I've been in a cast of actors in a play or on a movie set, and we've spent a very intense amount of time together, usually two things happen: we all get a cold and pass it around (!), and someone hooks up and becomes a couple. After the production is over, their relationship fizzles and they get upset. They thought it was love! However, they didn't have what it needed to keep it going after the parameters surrounding how they met fell away, because it wasn't meant to be an ongoing love relationship. They could have just allowed themselves to experience the intimacy of working closely together in an emotional environment, and to feel closeness, infatuation, and the chemistry, without taking it a step further and engaging sexually. They could have just had a casual physical liaison without expectations to keep it going, or trying to make it into something serious. But we are a touch-deprived society and afraid or unsure of intimacy in general.
And sometimes it's perfectly fine and healing and needed in some way to act upon these feelings, connect deeper with someone, and engage ourselves with them physically. Yes, even what someone observing from without might call a one-night stand can be the most healing thing in the world to the people involved. It's a matter of how connected you are to the other person and to yourself, your feelings. You ask yourself good questions. If it's just chemicals and a crush, are you willing and able to allow yourself to be immersed into it fully and know that later you may never see that person again or be able to take it further for practical reasons in your life? If it's someone with whom you feel a sense of oneness and connection to that well of love you have, can you handle the responsibility that comes with such an involvement?
So, there really is no one answer and no formula to tell you unequivocally how to know what to do. I think it just takes a certain amount of self-knowledge and self-examination. However, it does make things all messy and cheap if there is dishonesty and cheating going on. Communication not only lets the loved ones in our lives know what's going on, but it helps us figure out what we're feeling.
I hope this helps and doesn't confuse you even more!