Hi,
I can totally relate to your struggle to ever trust him again,
and the sandpaper tongue when kissing is a pretty big give away when my partner is doing coke, although I guess other things could cause that, but like you, I would struggle not to be paranoid about any of these things.
I guess all you can do is hope he is being truthful and know that if he is lying it will have a way of coming out without you really looking for it as a proper case of addiction becomes pretty apparent especially if you have already lived through all those lies already.
fingers crossed for both of you.