It feels like I'm the only one losing.

I know it feels like this now. I guarantee you this is not the case. You've actually gotten quite lucky. Yes, it's a shame that you had to marry this guy, but you're getting out before you've had children together. No custody battles, no child support payments.

I don't know who I am or what to do without him.

You're smart. You know this is one of the first things you should begin to figure out. It's a process, often times a long process. But you can begin it now. Just make sure that your definition of "who you are" doesn't include your work or profession. If your work is one the the primary things that defines you, it points to a lack of general growth and development.

I was on track before and now I'm not. I wanted kids within the next year, we had already picked names out for our kids. We were supposed to start trying this month. That whole dream is shattered and it hurts so bad.

This is the main issue: projection. You projected your life's hopes and dreams onto this man. Family, children, a house, vacations, life. Now you have to re-write this part of your life and it scares the fuck out of you.

This is why you should go to therapy. Address the projecting. It's important to ensuring you become and remain happy in your life.

From your stories and descriptions, he sounds like a giant douche tbh. You're pining for a guy who had an affair and takes you entirely for granted. Take the time you need to process all of this and focus on why you still want to build a life with him, knowing how cold and heartless he is.

From what you've presented above, this isn't someone you want to build a life with and I think you got lucky by having this decision forced upon you sooner rather than later. Because rest assured, it would have happened eventually with this guy.

Just my two cents.