It is possible that what I posted wasn't clear although I did want to know if you intended to try to scare him and as you explain, that was not your intention.
I would like you to consider though, even if it was not your intention, can you see how what you said to him COULD be interpreted by him to mean that he would lose access to his S, which COULD LIKELY scare him.
I am interpreting from you statement about being friends with your H, that you are afraid that if your H and you are friends, it may develop IN YOU, a desire to be MORE than friends. Is that likely the case? As you said, that's your past experience, so it stands to reason that COULD be your future experience.
Why is that a "bad" thing? Because you are afraid of getting hurt, yet again.
Do you have any other male friends that you look at and say, "he's a really good guy." Or have, even fleeting moments of wondering what a more intimate R with them might be like?
So it is fair that since you did not know there was an OP in his life, that wasn't a consideration in your thinking about why your H was saying what he was and acting the way he was. Now you know that. Even when the OP is gone, the AP will go through withdrawals, so they are not immediately going to come back to the BP. If they do, it would be rebound and a good idea for the BP to hold back. A rebound R can be unhealthy.
So if your H is in withdrawal, he is still likely to say he doesn't want back in the M.
He WOULD NEED to feel safe to go back to the M. AND... he would need to believe that a M with you would be DIFFERENT than it was when he began to want out of the M. Because THAT is the time he's likely basing his thoughts and decision to R on.
How can you provide that for him? Allowing him to feel safe with you as well as allowing him to see how a M with you would be so much better than what he's comparing it with?