Minderwiz
"My feeling therefore is that you might find him quite amenable to the prospect of working on the project but either you come across a better prospect or he's already committed elsewhere." could you please elaborate, i do not understand. thank you.
I don't see him working with you on the project you were thinking about but that is nothing to do with any adverse feeling on his part - the situation seems to be one of either you come across someone who better fits the requirements and use her/him instead or your original choice (him) is not available because of prior commitments. In other words if he turns you down it's nothing to do with what happened, he is genuinely busy elsewhere or you never get to the stage of asking him because you find someone with better 'qualifications' for that particular project.
For future projects I don't see any problem with asking him, he's quite happy to work with you and I'd say what happened is not in any way an issue. So if you have further projects ask away - if he says he's previously engaged, then it's a genuine answer. I think he would be quite happy at working together on a professional footing.