Ex-friend keeps asking for friend request on LinkedIn but I don't trust them?

I used to have this friend (I'm a woman and they're a man). We were quite good friends for a while but they started to get the wrong idea about me and our relationship, thinking I was romantically interested in them when I wasn't, and things started getting a bit heavy. It got to the point where it got very uncomfortable and it felt very awkward, because they didn't seem to understand that I just wanted to be their friend and nothing more. I ended up breaking off with them, even blocking their number so they couldn't contact me. However, for the past two years since I stopped talking to them, they occasionally ask for a friend request on LinkedIn. They don't seem to get the message that I'm not interested even though I am consistently ignoring and blocking them. It's a shame in a way that we're not friends anymore but I don't trust them to just be a friend, because I got back with them before after we broke friends for a while and they went back to their old ways, thinking I wanted to take our relationship further again. I don't want to be mean and tell them to get lost and I don't want anything to do with them because I think they're a creep, and a part of me wants to reconnect with them, but I just don't trust them. I get very nervous whenever I think of the way they used to treat me. They were quite manipulative as well, telling me things other people had said behind my back to get me to side with them, and I wasn't having that. What's the best thing to do?