How do you do it?

Long story short. I got into a relationship with a guy at work. I know it's not ideal. We had so much fun for over two years, and then a new girl started. She has had her title changed to Mx but has not made it public knowledge. I found out by accident. Well, it came out that this girl/boy goes for guys who are cheaters. My guy found out and started having a relationship with her. Trying to hide it from me. He's gaslighted me during this time. I tried to get the truth out of him, and he kept on lying still does to this day. Today, he said, "Let's draw a line under what we had." How do I get over this and not be bitter towards him and her/him? They are both on my team. I was also told about this from another colleague, and everyone in the team knew.

Please, no hate comments. I'm trying to keep myself together.