Should I tell her he’s cheating?

I met this guy that lives in my apartments about a month ago, we hit it off and started spending a lot of time together. After a week or so we sat down and had a conversation about the future, our intentions, etc. he said he was talking to a girl that lived 3 hours away, but they only text and talk on the phone, he hadn’t seen her in about a year, but he wanted to be up front with me. I appreciated that and kept moving forward. We got to a sexual point in our relationship where he was spending the night, introducing me to his family, etc. so when I told him I had feelings for him he confessed that he’s been in a serious relationship for 3 years with his long distance girlfriend. I feel betrayed because a serious relationship for 3 years and “talking” from time to time is two completely different things. I know if I was in her shoes I would want someone to tell me. It makes me sick to my stomach bc I would have never continued things with him if he would have told me he was in a relationship. I think it’s right to tell her, my friend thinks I should just let it ride. I’ve already broken things off with him, but it’s literally eating me up inside knowing he’s been cheating with me and I was unaware.

He came to my apartment today and told me that he “doesn’t know” what he wants to do so let’s just take it a day at a time. He’s not opposed to a relationship, but I told him I’m not interested. He kept leaning over trying to kiss me and I kept turning away. I finally came back inside and I don’t know what to do! HELP!!