Dislocation is likely a symptom of his mindset; Paul has had to become a creature of pragmatism, locking his emotional reactions into one purpose to ensure his survival. In civilian life, one need not be on guard 24/7, but Paul has forgotten this, and thus has difficulty with "ordinary" people, who cannot understand his experiences -- he no longer "belongs" in this safe, ordinary place.
Paul has had in so many ways to cease living a normal life in order to survive the brutality of war. This is something that is made clear in the earlier chapters. When he has the opportunity to go on leave, therefore, he finds he cannot disconnect from the lessons that war has taught him. This makes it impossible for him to reconnect to "normal" life and to pick up his normal relations again where he left them off.
One quotation emphasizes how distant Paul now feels from civilians. Indeed, he even feels a kind of contempt for them, since they have little idea of -- or little interest in -- what life is really like at the front:
When I see them here, in their rooms, in their offices, about their occupations, I feel an irresistible attraction in it, I would like to be here too and forget the war; but also it repels me, it is so narrow, how can that fill a man's life, he ought to smash it to bits; how can they do it, while out at the front the splinters are whining over the shell-holes and the star-shells go up, the wounded are carried back on waterproof sheets and comrades crouch in the trenches.--They are different men here, men I cannot properly understand, whom I envy and despise.
In terms of isolation, war creates a barrier between those who know about the death and destruction in military engagement and those who do not. I remember how hard it was for me to understand what soldiers were going through during the Vietnam War. I was young, but so were the guys that were dying or coming home physically and mentally changed. I had no way of being able to appreciate their experiences—and Vietnam was an especially horrible war, for so many reasons...very unlike WWII or the Korean War—from what I've read.
In terms of isolation in Chapter 7, one quote that might suit is...
"There is a distance, a veil between us."
For a quote, what about the part where Paul goes to see Kemmerich's mother. She wants to know how her son died. She is really anxious that she should know the truth. But Paul can't understand how she can care so much. He says
When a man has seen so many dead he cannot understand any longer why there should be so much anguish over a single individual.
This is a pretty clear indication of how Paul's feelings have changed and how different he is from a normal person.