Thank you for your lovely words, everyone, but I'm not sure how much it helps.
I've been thinking about this quite a lot today. I'm ashamed to admit that I would feel like I'd failed if someone was attracted to me for my personality. But at the same time, I know that that is supposed to be what is important. But actually, no, it's being slim, being pretty, having nice fingernails, being able to cook, looking younger than you are, having good (not big, just 'good') boobs and slim thighs... that's important. Or at least, that's what my mother always said and, it will come as no surprise to learn, in her eyes I failed at all of them. Stupid thing is that when it comes to everyone else I get that it's a combination of looks and personality, and that sometimes it can be just personality, and that when you're attracted to someone's personality you can begin to find them physically attractive. I get all that. And I get that someone who just looks nice might be a really unpleasant person... but when it comes to me it just doesn't seem to apply. I wish it did.
As for rationalising. I could write a book on it. I could probably equally rationalise the other direction, but that just feels like words. Whereas this way makes sense.
I don't think I even really feel down. Just a bit weary of it all. If I could just squash that little chink of light that keeps telling me that it might still happen, then I'm sure I'd feel better about everything. The problem is that as soon as someone says something nice or, like this man, tells me I'm "really lovely", or like my 'boyfriend', tells me I'm "beautiful"... etc... it makes me feel all warm and happy and I get a little glow of "just maybe..." and then I'm back at square one.
I've felt embarrassed telling people I have a boyfriend (or had - still don't know) because I think the idea seems so ridiculous. I'm embarrassed to have a 'boyfriend' because that suggests to people that I think I'm something special, when I know I'm not.
Izzy I know that what you're saying is 'right', but it doesn't make any difference. Especially when there are women who are 37 and still have the 'perfect' figure, pretty face, no grey hair or random hairs... I know they exist because I know one of them. I really do feel guilty if I'm with someone. I feel embarrassed for them that other people are going to see them with me and think that I'm the best they can do.
It didn't help that my exH did think he could do better than me. I wasn't allowed to meet any of his friends for a couple of years because I wasn't pretty enough. It was only when they started getting girlfriends that didn't look like the Italian actresses they lusted after either that he introduced me. If I'd had any self esteem at that point, I'd have told him to fuck off. But I thought that was all I deserved, and the best I could hope for, by that point.
So I don't think I'm quite as low as I was, but that's not really saying very much. 
Sorry I'm being a bit self indulgent and completely rambling. I'm also sorry to read that other people are also going through a tough time this week.
I think I have a pile of ironing to attend to