Back story to try and avoid drip feeding where possible (have NC for this).
DM and DF split when I was a baby. When I was 2 she met new P. He was an abusive twunt towards me and exclusively me, emotionally and physically. When I was 15 she finally broke up with him. She stayed single/casually dating for a few years until she met ex DF in summer of 2009. They were due to get married in November of last year which in itself was a revelation for DM who has always sworn her hatred for marriage! He was the kindest DP she ever had, he actually made an effort to get to know me and that was the happiest I'd ever known her, he really mellowed her out. Last year in February he died suddenly. Obviously a huge, devastating blow for us all but especially DM naturally.
Not to make it all about me, just trying to set the scene so maybe I don't look as batshit as my DH seems to think I am 
. First time dealing with grief as an adult for me (only other people close to me died when I was a young child so was pretty clueless), first funeral as well. I denied grief all of last year, I know denial is pretty common but usually denial that they're gone. For me I accepted he'd gone pretty quickly but denied that I was grieving, tried to brush it under carpet iykwim. Hit me like a tonne of bricks at the very end of last year and am just coming round now though it's clearly still fairly raw.
At the end of April she informed me she'd started seeing someone new, they'd gone on a few dates and so far so good. I was very pleased for her, she's still fairly young (early fifties) and I hated the idea of her being alone. She said he was an old friend of ex DF which I did find a little weird but still, I was happy for her.
4 weeks later it's DD's birthday. She wrote new DPs name in her birthday card. I cried when I saw it. It was still difficult having ex DF's name absent from cards but only four weeks after telling me she was dating someone new I see his name replacing ex's?? It really shocked me... A couple of weeks after this I noticed she'd taken off both her engagement ring and the ring she had made from ex's ashes, she'd also had a phone cover made with a picture of ex on (I always found it a little disconcerting but still), she'd changed that as well.
Then yesterday she text to say she was popping round to drop off something she had bought DS. No mention of new DP in her text. DP just wanders into my house as if he's a part of the family we've known for years, very sure of himself. Introduced himself, handed DS the gift and then took DC into garden to play with it. It all happened so quickly, I just felt so shocked! I think because I wasn't expecting him to be there and he just waltzed in. Then seeing him playing with DC, I just thought ex should be doing that and I fought back tears. I had to make an excuse I had mascara in my eye hence slight watering of eyes. When they left I sobbed for about half an hour. DH thought I was crazy. He really thinks I'm being overdramatic. He actually said "Ex has been gone for over a year now, it's time to move on." Which I couldn't believe, it felt so cold and callous.
DM and new DP also informed us they're going to France on holiday in two weeks. DH has to drive past DM's house to get home from work (which is most often late at night) and says he sees DP's car parked outside most nights so looking like he's practically moved in.
It just all seems so fast? Not the dating part but the fact he's already playing with my DC, is a name on cards, she's obviously removing traces of ex like the rings and they're going on holiday... I'm not only concerned for her but also my DB who still lives with her. He's 15 (abusive P is his dad) but it must all surely feel a little unsettling for him? To add another twist she still has ex's DD (8) on weekends. DM told me she didn't take the news of new DP well but she'll have to get over it (exact words) 
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I can't be the only one to feel this way. Aibu or just crazy as DH seems to think?