Dealing With Cheating...HELP!

So I’m in what I feel is a pretty unique predicament. My boyfriend and I have been together for a couple of years. We are in our mid twenties. We live together, we have a dog together, and all of that fun stuff. Oh, and we also work in a restaurant together. Our relationship hasn’t always been perfect, but there has never been anything we couldn’t work through. Over a year ago I started getting a weird feeling about him and one of our female co workers who also happened to be one of my friends. Rumors started going around that they were hooking up but it was never from a reliable source so I didn’t really think anything of it. I confronted both of them and they denied it. I stared getting really jealous though and eventually it got to the point where my boyfriend agreed to cut his friendship off with this co worker because I was getting uncomfortable. Well... I just found out about a month ago that they actually did hook up over a year ago and the whole time my boyfriend was saying he wasn’t friends with this chick they were actually carrying on a friendship and god knows what else behind my back. Being at work with them is so uncomfortable because since none of us want to quit our job we HAVE to be cordial. Recently she has been trying to make me jealous by sitting down after her shifts at the bar where my boyfriend works. He never talks to her but she just sits there and drinks and looks at him like a psychopath. I feel like I’m going a little crazy though. I get extremely bad anxiety every time they work together and I’m not there. Or I get anxiety when he’s scheduled and I’m not because I feel like she will show up and try to hang out with him while he’s working. I have confronted her multiple times telling her that she needs to back off but she’s relentless, and I want to trust him but he’s already lied about having a friendship and a relationship with her so it’s really difficult! Can anyone give me advice on how to handle this anxiety I’m having? Like has anyone been in a similar situation where you were constantly around a person who tried to ruin your relationship? I don’t want to break up with him because I truly love him and he has honestly shown remorse over the decision he made. It’s just hard for me to move on and work on trust again when it’s constantly in my face. Any advice or words of wisdom will help ❤️❤️❤️❤️