To be really struggling with my dad's new relationship?

[CallyT]

And I don't know how to deal with the conflicting feelings or change to the family dynamic

My dad started seeing a woman 4 months ago. The consequence was he and my mum have had this weird on and off pseudo relationship for years after divorce.

So they would go on holidays together and my dad would often spend time at her house/my childhood home.

After 15 years of this companionship he has overnight got serious about this woman. My mum has been dropped as a companion while he is off romancing this lady on lots of trips away etc. My mum is lonelier because of it although she needs to focus on herself.

He is giddy and expects me to be happy for him but I feel as though my parents have just split up! Last year they were on holidays and now I just have to accept that's all over and be happy for him?

You’re not being unreasonable for feeling this way, but I think it’s important to realise that it was a problematic way to go about their separation in the first place and if either of them were to find someone special again (which is completely normal) that this was always going to be inevitable.

To be honest, I think you should feel proud of your dad for treating his new partner with respect and consideration. It shows he’s a decent man. Can you imagine dating someone who’s carrying on with their ex wife as if they’re still married? That’s not ok and your dad is handling it correctly.

I understand your mum must always be sad and bewildered, but again, it was likely inevitable. She’s an adult and should have realised it was never healthy to have this sort of dependency on her ex husband.

@Didimum has absolutely nailed it. Your previous set up sounds horribly enmeshed and really problematic. Just because you’ve pretended your parents hadn’t split up does not mean he’s doing anything wrong in now forming a new relationship. Don’t punish him or his girlfriend for a totally legitimate relationship or you may end up ruining your relationship with him.

Why is this all on your dad, your parents are adults with independent thoughts and feelings

If your mum didn't want to be with him she didn't have too, it suited the both of them

Wow, that was selfish of your dad to keep your mum around if his intention was to find someone else.

Give over. The op's mother has agency over her own life. She chose to continue acting as though they were still together. No one forced her to remain so enmeshed with him.

So the mum had no say in it?

I think you need to reframe it and think how lucky you've been that they've both stayed so close over the years, you could have had decades of them being separated. You're an adult now so able to deal with it better.
I think it's nice when ex couples stay so close. It's the estrangement ones I can't understand when people have spent so many years together (unless abuse etc)
But I know it still feels sudden to you, maybe ask your dad to not mention her for a while?

Might be worth a conversation with your father that while you are happy that he’s happy - it’s a huge change for you from having your parents travel and holiday together to him moving on with someone new.

It’s ok to let him know that this is like a recent separation for you.

and plan to spend Christmas as separate families.

I think this is a good idea and a mature way of making your father aware of the impact this is having on you. Yes, you are an adult but you've been used to a situation of happy companionship between your parents that has abruptly come to an end. It's a shame your father didn't have the guts to tell your mum face to face that he was moving on.