AIBU to feel weird about my exDH and my best friend?

I’m sorry OP but it sounds at the very least like they’re having an emotional affair. A physical relationship seems likely to follow if it hasn’t already. Anything you tell her will likely be relayed straight back your ex and you’ll never be free of him. She doesn’t have your best interests at heart which she should do. Over my dead body would I associate let alone be dating my best friends ex. She has no class or decency. Dump her as well and let them have each other. Sounds very messy and you deserve to be as untangled as possible.

100% this. You absolutely cannot trust her.

Doesn't stop your stbxh and your bff from getting together. You said your bff and her dh have marital issues. Your H and your BFF are finding comfort in one another. You could call your H out on it - you're not divorced yet. Tell him it's utter bs he can't find another adult to chat to and a therapist is a good start.
You could tell your bff to at least wait for you and H to work out your separation before making a move on him.

You could ask her husband how he feels about them "hanging out." If you are going to say anything, do it now so you can move on without it nagging at you.

Regardless, your gut instinct is correct.
Make haste.

I mean you left him. He can do what we wants. I reckon he’s doing it to make you jealous. The best friend isn’t a friend. I would expect loyalty from her, you’re my best friend I come first. But seems they do want to shag or something is going on. Dump her. And only be civil to him regarding the house/kids, don’t tell him anything.

With everyone else on the "they want to bang" line of thought. Tbh I would be wondering if they already had. You've only just broken up with DH - why was that? Anything to do with your DH withdrawing or otherwise not engaging in family?

Regardless, look to other friends for support. She is no friend at all.

Every word you say will be fed back to him. Be very careful what you say in front of her.

Hasn't stopped anyone before. She was just waiting for yours to become available... leave them to it since you don't want him anymore. But don't confide in her- it will go straight to exh.

She's not your friend. I wouldn't see her or tell her anything you don't want your ex to know. She's not to be trusted.

She's married???? WTAF????

Well, with friends like this...
Whether they're together or not this isn't how a best friend behaves.
You need to distance yourself. Anything you tell her will go straight back to your exH.
Don't bother meeting her.
No need to go in with the accusations just drop her.
Do you have anyone else who can support you?
Fwiw my best mate and I have supported each other through divorce. At no point did either of us feel the need to be a shoulder to cry on for the other's ex.
Does your ex have no friends of his own?

She's no friend of yours that's for sure. Not matter what the outcome of their "drink" is - dump this friend.

A best friend is someone you can tell everything to, how could you trust her not go running to your Ex-husband.

People like her are treacherous. Her poor husband!

And obviously poor you :(

Does her husband know she’s been texting with him?

Does she know your husband wants to get back with you?

I’d be done with all of them.

Maybe she wouldn't mind you messaging her husband and arranging drinks with him? 😊

What's her husband like?

She is no friend of yours OP. Married or not, she's acting weird and I would expect her to be supporting you as her 'best' friend, not arranging to go out for drinks with your ex. I think she's behaving horribly.

My exDH doesn’t want to separate and keeps trying to convince me to come back. I’ve been clear I’m done.

My best friend of over 20 years has been pretty quiet through all this.

Then she messaged to say she’s been talking to exDH and they were planning to meet up for a drink. She ended up cancelling the drink with him.

Then I found out they’ve been messaging each other a lot more than she’s been messaging me

Opps forgot to mention her husband. Married for 8 years.

So why doesn’t he go out for a drink with her husband?

Bloody hell.

Your friend should be looking for ways to support you. Maybe she doesn't agree with what you've done, or how you've done it, but she should still be looking out for you before your ex. You should be able to rant to her without worrying that she might feedback to him.

Sorry OP but it doesn't sound good

That is not on at all. She is no friend.

My friend and her husband got divorced. I was friends with both but she was my priority.
He'd message me with innocuous things. Replied likewise. He'd always mention a drink though. I just blanked that bit.
Then he messaged - when are we getting together for that drink then?
We're not.

Slimeball.

Thankfully, they're both happily married to other people now!

I wouldn't immediately jump to the presumption they are/want to bang, but i would say it's pretty clear your so-called Best Friend has "picked sides" and it's not yours.
I'm sorry.

Well your 'friend' isn't, is she? Also she's stupid because I'd bet anything your ex wants to shag her to get revenge on you.

I'd let them get on with it to be honest. Scuzzy pair.

This happened with my DM and my DF except my fathers affair with her best friend of 25 years started a few weeks before they split.

I’d be laying it out to your ‘best friend’ that she isn’t being very supportive, completely disloyal, and it is pretty obvious she’s pursuing something with your very recently soon to be ex husband.

I wouldn’t be entertaining the saga of him dropping her off to yours.

Give her one opportunity to see her blind stupidity and grovel for forgiveness, otherwise sack her off like you did your ex.

I feel terribly sorry for you, the level of betrayal from a close friend is very hard to deal with.