Zoo33, I've been reading your thread and cheering you on. You are doing amazingly.
PLEASE STOP HAVING LUNCH WITH HIM
I know that you think you can just ease yourself out of this relationship, and that it would be "too hard" or "unkind" to just cut contact, but that is nonsense.
You are in a very dangerous place - he is taking you out, promising marriage, suggesting you guys elope and confident he could talk your mother round - and you are going along with it.
I know you think you are "telling" him that he's crazy, it's not going to happen, it's over, mostly blocking his contact, etc but what are you SHOWING him? You are showing him that you still prepared to spend time with him, share meals with him, discuss your relationship with him, etc.
You do not need to speak to him ever again. You should not have conversations with him EVER, let alone ones which are long enough for him to suggest eloping and for random women to be so concerned by his behaviour that they slip you notes in secrecy (because she can tell from five minutes of your conversation that he would try to prevent that).
I am very very worried that one day you are going to stop posting because you have decided to go back to him - and not exactly because you want to. He is doing his best to convince you that splitting up with him is impossible - he will try to wear you down and thwart your efforts to get away, and demonstrate that he will not give you his permission to end the relationship, that your reasons for wanting to end it are insufficient and can be discarded, and that he promises to change and you ought to accept that, and therefore you will have to, eventually, give in.
Have you seen the film Labyrinth? Think of the bit at the end where the goblin king promises Jennifer that all her dreams will come true if she will just let him rule her. It's the bit where (when you're a kid) you're screaming at her not to trust him, it's the final battle of wills between them and her resolve is wavering and you know if she gives in she will be trapped forever? Finally she remembers the final part of the spell, that her will is as strong as his, and her kingdom as great and that he has no power over her.
He has no power over you. Be like Jennifer :)