Ride the Line by C. S. Silverne

Life had a way of being beautiful—until it wasn’t. Unexpected loss left each of us stuck in our own quiet versions of punishment and longing.
Until one offhand comment over drinks unraveled everything. Changed everything.
Maddox.
Zander.
And me, Marley.
One night. No past, no future. No strings. Just whatever we wanted, with the understanding that we could walk away if it didn’t work.
Maddox and I had already sworn our vows years ago. We’d be fine. For better or worse.
Only this time, the risk turned out to be for the better.
We never anticipated those vows would one day include his childhood best friend… and my dead best friend’s husband