The Last Days of Summer by Sarra Manning

Sometimes all it takes is one long summer weekend for the person you thought you hated to become something more…

After a disastrous first meeting, Cassie and Marc become arch nemeses. He might have great cheekbones and a sexy French accent but he’s a terrible person who did a terrible thing. Too bad that Cassie’s best friends Lucy and Russell think he’s wonderful.
But years later, when an unexpected tragedy strikes their friendship group, Cassie and Marc team up to give Lucy and Russell the best weekend ever so they can make new memories with all of their favourite people. Which means convincing everyone that Cassie and Marc are head over heels in love.
After hating him for so long, it takes four bittersweet days for Cassie to wonder if she got Marc all wrong. Can they let go of their troubled past and together, face whatever the future is going to throw at them?