I would be surprised if your mother and other older relatives would countenance this Probably not, as my Mum would rather her not be there and my only other older relatives are my Dad's Mum and my Uncle and Aunt on my Mum's side. DP's side neither know nor really care about the situation.
that there is no big insult/barrier (affair for instance) that people would understand There is in as much as people who know the history well think it's weird he remarried anyway when he didn't seem that into his now wife and everyone felt he was not over (and possibly still in love with) my Mum. Most people (my Aunt and Uncle, my BiL, etc) regard the relationship as odd.
it's doing a nasty thing where doing a nice thing would be easy (in fact, expected) It's not going to be easy when I know it will make the day difficult for my Mum, Sister and Grandma.
Are you saying that you aren't going to have any kind of ceremony whatsoeer? Or that you aren't going to invite your dad? Because no matter what size celebration you have, 20 people or 200 - the bottom line doesn't change - if it includes your dad, you can't justify not including his wife. So the only way you get to have your way is by not inviting your father.
Yes that's what I'm saying. Just DP and me and some witnesses.
Or by just coming out and saying "I know it's terrible, but I just don't want her there", and giving up the moral ground. But I never claimed to have the moral ground here. I don't care how I look to people, I just want there to be the least upset on the day and during the build-up.
Is this woman really so important to you that you will change your wedding ceremony just to avoid her being there? If it means that my Mum and indeed myself doesn't have the inevitable anxiety that inviting her would create, then yes, I would.
When you have guests, that makes you a Host, a Host's job is to make guests feel as comfortable as possible That's right, and the comfort of my immediate family is more important to me than that of a lady I barely know who my Dad felt obliged to marry so he wouldn't be lonely in his old age.
I have no desire to get to know her, as I'm sure she doesn't me. As I've said times, we don't have a relationship and that suits us fine.
by not inviting your father's wife, you are putting him in a very difficult position, making him very uncomfortable, not just on the day, but long into the future, I've said I'm not sure if this would even be the case. He might in fact realise the awkwardness of the situation and appreciate it would probably be easier for all parties were she not present. I don't know this though. Say it were just parents and a couple of friends, a wedding party of 8, then would you all understand more why is is difficult to have her there? Well to me that room of 80 is as intimate and close as the 8.
OP this seems to have gone from 'a preference not to have her there' to guilt tripping your dad by telling him that you can't have the wedding you want because of his wife. A woman you've barely spoken to, and who hasn't done anything wrong! She has done wrong, she's alienated people I care about. She has made no effort to form a relationship with me, which is fine, I do not wish to have a relationship with her.
The reason I've decided it's probably easier all round to completely rethink the wedding is because I honestly wasn't expecting for it be deemed so universally despicable to consider finding a way of not including someone at my wedding whose presence would make the day less enjoyable for myself and others.
I'm pretty soft and laid back on the whole. If it were just me I'd probably have caved by now thinking, oh well, I have no time for the woman, but maybe we'll work it out so that it isn't an issue. But knowing how my Mum, sister and Grandma feel makes it not so simple.