I know that he’ll want to help. I can’t stop thinking about the way he was that day in the car, about how things felt
What does "about how things felt between us" mean?
Source: The Girl On The Train, Paula Hawkins
The word "things" probably refers to the feelings between the two (for each other). "Things" could feel tense for example. If the person can't stop thinking about it, perhaps it was sexual tension, or some 'negative' feeling.