adult son with girlfriend living with us

[HJC63]

Hi everyone
I was hoping for views on an issue that is really bothering me and I'm wondering if I am in the wrong to be upset.
I have 2 adult sons living at home. My eldest was probably going to move out with his girlfriend but lost his job after Covid is now back at uni.
Nearly 2 years ago my son and his girlfriend could stay with us for 10 days . It was the height of Covid restrictions and she couldn't find somewhere to stay and was starting a PG uni course. We said of course. 6 months later she was still here- nothing said. They both then said wanted to pay something towards costs which they did. We thought- well she must be staying. Scroll on to last week when after the girlfriend and my younger son had words. He said something to her- she thought it was a more serious word and so she got upset. she said she wasn't welcome in our house. Apparently I also didn't make her welcome in the family because when I discussed the future I didn't include her (true because I didn't know if my son was going to include her in his future!)
Last week she just came into the room , dropped the keys on the table and said she was leaving. She all packed and so she went.
Did I do wrong in way? I was annoyed because she went through cupboards taking stuff and never said anything. I did say to my son that she have at least told us in advance. He is on her side now saying that he now doesn't feel welcome. I have agreed to pay for uni course and delayed my own retirement to support him and feel hard done to .
Am I wrong?

Nope, she sounds like an entitled nightmare, as does your son.

When you say she went through cupboards, do you mean she packed her own things in advance so that she could make a dramatic exit, or that she has taken some of your personal/household items to furnish her next home?
Or was it e.g.: some tinned food and toiletries to start her off because she has been contributing to food and grocery bills and so considers the stock in the cupboard partly hers?

I don't understand this situation went from 10 days to 2 years without a conversation.

well, yes, your extremely poor communication led to a situation where everyone was resentful

No idea. You haven't given any clue if you guys have gotten on well before they 'had words'.

Your entire family appears to have poor communication skills
your younger son should've stayed in his lane
yoy should've spoken about this somewhere after the initial ten days

Show him this disscussion. You know that you were very fair and generous. You might have to wait until he can appreciate your point of view. Keep being positive and hopefully your son will have a close relationship with you again soon. If he moves out just keep the door open - invite him and girlfriend over for a meal once a week etc.