Its infatuation. It normally happens because something is lacking in your marriage. If there is anything wrong in the marriage you need to focus on fixing it. Keep your distance from this man. Its a silly crush and its not worth ruining your life for. People who have affairs lose everything that matters and always regret it. He is just a fantasy-reality with him would be a lot different than you imagine it to be and it would never work. You need to put all this time and effort into your marriage. Book a romantic holiday now with your husband-you need it. Start doing date nights, buy a sex game. Bring that hunger, drive and desire back. Play a game with your husband-pretend the two of your are having an affair and meet each other for quickies throughout the day. When something is wrong with your marriage-the bedroom is the best place to start fixing it. Aim to have sex everyday for 30 days-it will bring you really close. Aim to try all the positions in the kama sutra-it will be a lot of fun.
Then you can focus on any other issues such as lack of communication, affection, quality time, romance. Whatever needs to be fixed. Tell yourself now your marriage is in danger and it is your job and your mission to fix it. If you are putting all your energy into not losing the man you love-it will push this other dude out. You have to distance yourself from him. Ignore him as much as you can. Act busy when he is around. Give him the message you are not interested.
Look up emotional affairs, thinking the grass is greener, infatuation vs love and anything else you can think of to get this man out of your head. If that doesnt work-quit your job or get a new one. Its a crush, nothing more, nothing less. You love your husband and should not take him for granted
"Don't ask a question if you can't handle the answer".