I really don't know your sitch but here is my two cents: You are in piecing!!!!! This is where every single one of us that comes to that board wants to be eventually. You got that far. That's something you were fighting for a bloody battle and don't you even think about giving up now.
I am hot tempered (one of the 180s I'm doing is self control) and I'm quick to react and then be sorry for it when it's too late (can't take it back - tried it and it did not work). So take a deep breath, count to whatever or say opposite of what your H would normally expect to hear. Or just say something totally unrelated! Like cheese! Flower! Palm tree! WHATEVER! If he asks just say that you recognized that you were going to over-react and you did not want to do it - you will both get a laugh out of it (the more silly the thing you say the more laugh you'll have) and it will help.
Do a lot of AS IF and still don't believe what he says (okay, be selective, don't believe the bad stuff only ). When it comes to past - don't bring it up. You knew that once you get to piecing you won't be able to because otherwise you'll get stuck in the past - that's where our WAS are and that's a bad place to be. You made your choice fighting that long to burry the past.
You can ask him about reassurance for the now and for the future. Neither he nor you can go back in time and fix stuff. Leave it there. He doesn't have to go out of his way but let him know that him showing appreciation for you (words of affirmation or whatever your love language happens to be) will work the magic. He just needs to know that. If you feed him the stuff you won't believe in it even if he does it. Just like coming back had to come from him so does the reasurance.
Hopefully that helped a bit...and I know, easier said than done. Just know how many people (including me) would kill for the chance to be in piecing....