Been there, done that and got the teeshirt.
Oldest son's now ex-wife. Family had a similar background, both father's in the military, German background in one parent each. We are married, hers were divorced.
High School Sweethearts. We tried our best. We really did. She had a terrible relationship with her mother, so we gave her a room in our home. She needed money for a course to start a small business, we provided it.
They eventually moved into an apartment (that we later found out her mother owned). Our son paid the living expenses, bought the furniture and made sure she had funds for whatever she wanted. Her mother bought her car, her father paid her cellphone bill (this was still happening in her late 20s). She never held a job for more than a few months (thinks coffee and chocolate shops/retail).
They decided to get married, at this point we'd never met her father (10 years of being together). Met her Mum twice. She promised to take me with her to buy her wedding dress. Nope. Got told about it afterwards.
He dad gave her 1K for her dress, hair, etc. Our son paid for the dinner and the hall. We paid for all the alcohol and the buffet at midnight. We were allowed to invite two non-related couples. I thought fine as I knew they were trying to control costs. Her Mum had six coworkers and multiple personal friends invited.
Her mum accepted all the thanks for a great evening.
After the wedding, she decided she had fibromyalgia and got herself a cane.
The girl was and probably still is a lost soul looking for something but what it is we can't tell you. She had a Goth phase, a prepper phase and took up canning and fishing for their food. Then it was an interest in Norse mythology and had elements incorporated into their wedding ceremony.
She walked out on our son six months after the wedding stating "marriage isn't what I thought it would be". I know no one knows what goes on inside another couple's relationship but so many saw red flags and all we could do was be there when it imploded.
Our son is much happier without her. His personality is coming back. He's always been a nice man, it's just nice to see him with his own interests and without worrying about her.
Oh, and the final red flag? They went for genetic counselling due to some health issues in both sides. Basically, they were told as a couple they had a very small chance of having a healthy child (CF, CP, autism on her side). So my son suggested adoption, fostering, or even a donor egg. She wanted to take the chance to have "her" child.
When she did leave, she left our son with all her pets to look after. As he said, "at least we didn't have kids, she'd have left those behind as well".
Just be there because when it ends, your son needs love and affection, not blame.