With that much experience and that many relationships, I would hope he's very good at communication, so my advice would be: talk to him. Tell him about your concern, or even show him this post. See what he has to say about it. I would think that the person most qualified to decide if he has time for another relationship without short-changing/hurting anyone is him.
Also, since you already obviously have a connection to him and want him in your life at least as a friend, I would think giving a relationship a try would be good, if that's what you both want. At least then no matter how it went you wouldn't spend years wondering "What If??" (yes, I know this is a slightly selfish attitude and I applaud you for being concerned about the other people involved, but you can't live your life true to yourself if you're making your decisions based solely on OTHER people's needs)
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack