There are two ways to deal with this.
1: muddle through
In this scenario you feel at the mercy of emotions/feelings beyond your control ("all consuming") and go around telling yourself and others that you don't want to feel like this but you just don't know what to do... End up at socials because, hey, it's a work thing so it's legitimate right? And eventually find yourself getting deeper and thinking about him even more, until thoughts of him have pushed your DH out almost entirely and you and DH are in a some shell of a marriage which you have emotionally detached from some months previously, all the time claiming you had no idea what you were doing.
Unfortunately I and other posters on here are telling you exactly what you are, in fact, doing (even though you might kid yourself that you aren't), so you won't be able to tell yourself that lie any more.
2: deal with it.
If you aren't too sure what this entails let me explain.
Avoid any contact with him that you can.
Do not go to socials.
Do not spend any energy finding out if he will be here there in this meeting that meeting so you can find yourself " accidentally" in his presence.
Never ever drink with him. Not even if you are celebrating a work success or failure.
Never discuss you personal life with him.
Never discuss your relationship with DH or his other half at all - this is an act of betrayal.
Never confess your feelings to him. This will take you both down totally the wrong road.
You need to establish openness with DH (windows) and impenetrable boundaries around your exclusive relationship (walls). Yes, even when your relationship is in a slump. Especially then.
Change your role or job at the next opportunity. It might take a year but you can start looking now.
Do not daydream about him. Believe it or not, you can choose not to. Google it and find a method that works for you.
Definitely do not fantasise sexually about him.
Absolutely definitely never fantasise about him while with your DH. This is a heartbreaking betrayal.
TALK TO YOUR DH. If you say to him: you know honey I feel really silly about it but I keep finding myself having these crush feelings on this guy at work and I wish I didn't feel this way but I didn't feel right keeping it a secret from you and I'm telling you because I love you and I want our marriage to be a good one where we are honest with each other even about difficult things. You might be amazed to discover that he loves you SO MUCH that he is willing to be understanding about it. And I promise you this will burst the bubble of your crush and you really won't feel this way again.
Sorry for the rant and sorry if I sound angry. I followed path no 1, it's a complete mess and I only have myself to blame, so if I sound angry it's only cos I'm angry at myself. I would hate to see you go down the same path. Trust me, at this stage it's early enough that you can catch it without devastating your marriage. Carry on and you won't believe how quickly it can get out of hand. The pain and suffering that can come out of these situations is beyond the comprehension of someone in your situation. Google " emotional affair" or go to emotionalaffair.org and soon you will have your eyes opened. Also look up "limerence".
Good luck. You sound like you want to do the right thing by your marriage.