Not sure if anyone knows this- reckon I read it in about 1990 ish. This was a teenager/young adult book. I can't remember much about it other than it is from the point of a girl whose father had died recently. It was set in America. I think the Mum announced she was 'leaving' the Dad and stopped wearing her wedding ring as she found out that he had been having an affair before he died. I think the Mum got together with his friend. There was something about a beach trip in it. I'm pretty sure there was also a pickup tryck, and there may have been something about a dog riding in the pickup truck with its head out of the window.
Thanks!