The New York Times has an excellent article on the challenges faced by couples after one member survives brain injury.
Carers sometimes say that, after brain injury, their partner is emotionally unresponsive, emotionally unstable or that their ‘personality has changed’.
This can lead to a strain on the relationship that far outlasts the ‘obvious’ effects of the injury and, unfortunately, the problem is not widely recognised.
Mrs. Curtis, 60, was once drawn to her husband’s “sparkle,” she said. After the injury, he “flat-lined” emotionally, and he suffers from depression, anxiety and a lack of motivation.
Her husband sometimes makes erratic decisions, she added, like the time he decided to take a do-it-yourself approach to the plumbing at their home in Coralville, Iowa. “Not a good picture when I got home,” Mrs. Curtis said. “And you can yell at him like a little kid, but he didn’t know any better.”
Once a software programming analyst, Mr. Curtis, 57, has “a lot fewer interests” than he did before the injury, and he estimates he has lost 90 percent of his friends.
“It’s a new you,” he said, “and they just can’t cope with that.”
The NYT piece looks at some of these difficulties but also the work of rehabilitation psychologists Jeffrey Kreutzer and Emilie Godwin who are developing ways of helping couples in this situation.
Link to NYT piece on relationships after brain injury.
Mind Hacks 
This is the topic of my PhD (which I am currently trying to write up).
In a nutshell, it seems that changes to people’s personality and self control are much harder for relatives to deal with than physical disabilities, or other cognitive disabilities like memory problems or problems with speech & language. Of course, these other problems are also difficult to deal with, and every couple is different, so its very hard to measure the impact on a couple and their relationship in a quantitative way. For this reason, half of my research is based on qualitative interviews with family members of brain injured people.
I should also take this opportunity to promote Headway, a charity for brain injured people and their families, with whom I’ve worked on and off with for 6 years now as both a volunteer and an employee. Headway do a lot to give social support to both brain injured people, and their families. They have branches in many parts of the country, and anyone reading this article who has a brain injury, or a brain injured family member, can find a local branch on their website here:
http://www.headway.org.uk/