Is there a better word or idiom describing someone who is stuck in the past?

I know a question with similar phrasing has already been asked and closed but what I'm looking for is not something in the line of "nostalgic" or "old-fashioned" or any other way of referring to individuals who are out of sync with popular ideas, opinions, values, belief-systems and etc.

The condition I wish to find the term to refer to is about individuals who as a result of trauma or a significant loss, are found to be reaching for the same thing over and over and over again, even though the initial motive is long outdated, irrelevant or etc. or individuals who are often daydreaming about how their lives would have looked like if this or that event hadn't happen that way, and not only "daydreaming" but that their real life is within those fantasy realms and in real life they are unable to find suitable alternatives for what was once the real drive for in that past time.

For example, on the dysfunctional end of the spectrum you might call them "helpless", "listless", "disoriented" and etc.

But the term I'm looking for is regarding the ones who seem functional on the surface, because there are people who are living normal lives, but when you get to know them on a more personal level, you realize the reason they rejected that career offer was because the career they wanted to pursue was the choice their parents denied them at youth, or when you asked them why not going on a date with that person, the answer is that "I have already loved someone, I can't ever love anyone else. What would be the point of all the hassle, if you can't love that person."

Off Topic Example

For example, the "nice guy" trope is often exclusively used about individuals who want to have all the ladies but are incapable of understanding that the dating dynamics is more complicated than just being "nice" to someone who is attractive.

In the same style, the individuals I'm trying to find the right label for could be considered full of regret, resentment, rancor over the past, but not directed at a group [rightly or wrongly] rather that these emotions are so strong that there is no place left for having feelings about the things in the present or possibilities in the future.

For example, someone who goes on the same spot he or she met the [perceived] "love of his or her life", after having lost that relationship, either in the hope that he or she would also show up, or otherwise if it is the loss of the individual, then in the conviction that it is only in this place that if ever a new person can fill the gap of the deceased person, otherwise meeting someone elsewhere can't be ...

PS. For the sake of the requirements for "single word requests" here is how it can be used in a conversation:

A. Oh, I just met XYZ; He seems like a very intelligent person! why didn't you tell me about him before?

B. Oh dear! He is quite ..........! Two years ago, Lady Catherine was almost preparing herself to be wedded to him, in fact, we all were; But she was no Elizabeth! When death couldn't convince him to look for someone else, you, my young and inexperience girl, would just be wasting your time on him!

Solution 1:

Haunted

2: preoccupied, as with an emotion, memory, or idea; obsessed: His haunted imagination gave him no peace.

Or, another example sentence: He was haunted by the past.

Solution 2:

Cambridge Dictionary has a quote against the word 'embittered' :

He died a disillusioned and embittered old man.

I think either or both of those descriptive words fit your request.

The severe case, when Post Traumatic Stress Disorder is evidenced, causes people to continually re-live the traumatic event, and/or attempt to rationalize the whole background of the situation in order to obtain closure.

They are truly 'stuck in the past', their memory and mind revolving perpetually around a past from which they struggle, sometimes for years, to be free.

But if you are confining yourself to the generality of humanity who simply regret lost opportunities or feel remorse for wrongdoing, then I think the Cambridge quote is quite suitable.

Solution 3:

One person mentioned "haunted," which I believe is a right fit. However, it doesn't seem to fit your "one word requests" example. A closer cousin to it in my imagination would be "wistful."

wistful (adj.) sad and thinking about something that is impossible or in the past: I thought about those days in Spain and grew wistful.

Source: https://dictionary.cambridge.org/dictionary/english/wistful

Oh dear! He is quite wistful! Two years ago, Lady Catherine was almost preparing herself to be wedded to him, in fact, we all were; But she was no Elizabeth! When death couldn't convince him to look for someone else, you, my young and inexperience girl, would just be wasting your time on him!