Feeling a bit sorry for you OP - you didn't ask for a barrage of messages judging the way you are interacting with this man. These are weird times, and it must be so hard for people who are trying to date. My view, for what it's worth, is that there is no harm in enjoying the sexy online interactions, especially since it sounds like you're being cautious about what you send. And so what if there is no chemistry when you do finally meet? Might work to have a first meeting somewhere reasonably neutral and non-committal (coffee rather than a romantic dinner?) so that it's not too awkward to leave early if you want to.
Im really sorry to hear that you're so unconfident about your body. Two stone overweight does not sound awful to me - not every man finds skinny women attractive, and plenty prefer a more rounded look (even if that preference is viewed in the mainstream as a bit fetishistic!). If he's seen recent full-length photos he presumably has an idea of your dimensions even not having seen you naked? Maybe you could try to start a conversation about what sort of women he finds attractive - any celebrity crushes etc. Might give you an idea of his general preferences. And if he picks a load of skinny people you could say something like, 'Lol, I hope you realise I'm not as thin as her' ... you might be able to judge something from his reaction (though it would probably help to run it by a trusted friend, since your anxieties in this area might make you read negativity into anything ambiguous).
It might be that the real problem here is not your body but the effects of your husband's affair and the fact that you haven't had sex in a while. I'm sorry your husband put you through that, and I think it's common in that situation to compare oneself to the other woman and conclude that you must be inferior. That's simply not the case ... people have affairs for all sorts of reasons that have nothing at all to do with the attractiveness of their partner (and often have affairs with people who are much less attractive ... I'm thinking of those stories from years ago about Wayne Rooney shagging women who were much older and less attractive than his partner!). Having sex for the first time in a while can be difficult, I know.
I don't think you should feel like you have to lose weight before you meet this guy - but maybe it would help to try to do things that make you feel good about your body, for your own sake, not his. In my case I find exercising has this effect - it just makes me feel healthier and stronger, and therefore better about my body, even when my size has not changed at all. Just getting out for a longish walk could make a difference (not much else to do at the moment anyway). Or Joe Wickes's YouTube workouts. Or something completely unrelated to exercise if that's not what does it for you ...
And let's not forget that while you're worried about him not liking you, you're ignoring the possibility that you might be disappointed in him. You sound like a fun and smart person whose usual confidence has been knocked by an arsehole. That doesn't make you any less worthy, and if you and this guy end up not liking each other, there will be more opportunities and this man will have been a useful trial run :D