I have a crush on a married man at work, but I have a boyfriend.
I really hope you have thought this through. What would be some consequences of getting involved with him?
I might lose my job and not be able to afford my tuition fees.
It's okay to have a crush on someone, but it sounds like a very bad idea at the moment. Both you and your coworker are in relationships, and selfishly getting involved would destroy two relationships. In addition to risking hurting yourself financially, you could impact the kids ability to have a good home with two parents.
Who cares? I have to have him, I have no choice.
If you can just be faithful when you are in a relationship your life will be much simpler and have less drama like this.