I know that what they specifically talked about makes a difference so here is some of what I found.

I found a text exchange where he was talking to her about whether or not to leave our marriage. Three days before this conversation (last week) he told me in therapy that he was "All in" on our marriage and really loves me.

To his ex wife he said
"I've been thinking about it for months"
"I don't know how vindictive she will be"
"I may be in a hotel on wednesday after I pick up the kids"

She sent him ensouragement to leave and appartment listings.

He was at his parents house having a mans weekend with his father and two sons at the time of this text exchange. I stumbled on it when he got home.

I feel so betrayed and like he cheated.

Am I wrong to think this is a cheating type betrayal??

If he talked to his father about concerns and looked at appartments and options I think I would feel differently. More like - if that's really what you are thinking then let's talk about it

Where because it was his ex wife I feel like there is nothing left to talk about.

Thoughts? Advice

Should I just cut my losses at this point and move on?

I can understand it hurts, but it isn't cheating. He is very confused or not honest and open about his feelings to you.

He’s clearly planning his exit from your marriage. If you get a chance to access his phone again, add her as a contact, then block her calls and emails! She’s maybe trying to worm herself back as his partner again. If she hardly knows you, why would she be actively encouraging him to leave you by sending him details of apartments?!

Your husband’s use of the word ‘vindictive’ is interesting...and also concerning because he’s already ‘othering’ you by making you into a problem who will be spiteful and revengeful if he leaves you. That’s not a nice thing to be saying to his ex about you. It seems as if he already sees you as a potential adversary.

Talk to him. Find out what his true feelings are about you. If he’s saying one thing in therapy, but then doing another...well, like they say ‘actions speak louder than words...’ If he loves you, he needs to show commitment towards you and ditching his ex is a start! There’s only room for ‘one main woman’ in his life and it’s either you, her or someone else he runs off to...

I don't think that's cheating, but it's definitely a red flag. A big one. It seems that he's seriously considering the end of your marriage. Of course that conversation being with his ex-wife can make you feel even worse, but I think the problem is not her, is him thinking about leaving. You should try to talk to him about that to figure out if it's worth to keep trying.

It’s certainly a betrayal. I understand needing to talk to someone but talking to your ex about something like that is taking it too far. Very poor judgment. If you can’t trust him not to do that I would wonder what else has been said.