How can I request my boyfriend to stop bringing one of his friends around me?

I've been dating my boyfriend (24M) for 8 months, but our relationship is somewhat complicated due to our past from a situationship 6 years ago that lasted for 2 years before I cut off contact. We reconnected about 9 months ago, allowing me to reestablish friendships with some of his friends as well. Approximately 5 years ago, one of his friends (24M) asked me to accompany him to a party since he didn’t have a date. We were friends at the time, and I agreed under the condition that nothing inappropriate would happen. He assured me of that, claiming he’d never disrespect my boyfriend. However, later that night, while I was asleep, he decided to act differently and attempted to rub his erect penis against my back. I immediately rolled away, left before he woke up, and ended our friendship by removing him from all social media. When I confided in a girlfriend about this, she shared a similar experience with him, which helped me feel more determined to sever ties. Years later, I still had feelings for my current boyfriend and reached out to him. He was thrilled, and we eventually began dating. Early on, he mentioned his friend, which made me uneasy. I didn’t want to elaborate, so I simply expressed that I didn’t particularly like one of his friends. My boyfriend said he didn’t want to know any more details, so I left it at that. The friend moved abroad for a time, but he’s recently returned, and I’ve had to interact with him a few times. It’s been awkward; he acts as if we’re close despite our history. My boyfriend mentioned him in front of a mutual friend of ours who also had a negative experience with this guy, and when he suggested they would get along, my friend quickly said, “No, we don’t like [his name].” However, my boyfriend didn’t pick up on the hint and continued to speak highly of his friend. My friend believes I should tell my boyfriend the truth—that his friend isn’t as great as he thinks. I'm unsure how to approach this topic. I worry about potentially upsetting my boyfriend or making the conversation take a turn that could hurt me as well. I feel guilty for withholding this information, but I'm at a loss about what to do. Any advice on how to handle this situation?