There's nothing I can see in your post that points to you doing anything wrong. We all have pasts and if he can't accept your past then I honestly feel like he's not accepting you as a person. Some of us are more comfortable with sexting and other sexual behaviors than others, if he has an issue with that that is on him, not you.

If it was me, I'd sit him down and talk to him about it being your past and he is your future. If he can't separate the two and see that you've corrected the error (the STD. And besides, you were open about it in the first place.. points in my eyes) then maybe you two can't move on until he can. You've accepted his past (goods and bads) and you deserve the same amount of respect that you're giving him.

I can't tell you what to do (besides, I'm just some stranger on the internet so why listen) but if it was me in your position, I'd leave the relationship if he couldn't accept it as something that's a part of who I am that I've moved on from. If he has a problem and he can't move on he might never move on and may always hold this over your head. Not a healthy thing in a relationship IMO.