FWB Turning into something more?

So I’ve been talking/hanging out with my ex for quite a while now, about 10 months. We started off as FWB and quickly developed feelings for him… shocker. Anyways, we continued with our arrangements and sometimes I would joke around about wanting more. He’s told me that he’s had feelings for me too and other things to hint that this could go somewhere more but we never really took the initiative to do anything about. I wanna be honest so I can get the best advice so I wanna let you guys know that we are very on/off. We fight a lot but they’re mostly petty arguments that are over within minutes. However then there are serious ones where I say I’m done with him only to take him back when he begs me to. I finally had a very transparent conversation with him about what it is that I want from “us” and if he can’t give me that then I’m done. He ended up calling me and he told me that he is willing to put more effort in, communicate better, and we even brought up the idea of exclusivity. However, all these things were reassuring to hear but it is not the first time I’ve heard things like this from him. I told him that I’ll give him a chance to prove to me that he’ll change but he has to do that without seeing me because I know that will only lead to sex. He said that he can’t really say anything but words and he needs the chance to act on it and show me which I understand to some degree. I know I can obviously meet up with him and not have sex but I just know us and we will probably end up having sex which I don’t want to do as of right now. What are some ways that I can allow him to show me he’s serious this time without seeing him? I just don’t trust what he says at the moment.