Only the Lonely. Angelfire Series, #4

Mikey Lund has spent thirty years being the odd man out and believes he only fell into being in a popular crowd as an adult because of a friendly association at Foxx Body Shop, where he's the head mechanic. Truthfully, he's been in love with most of his female friends from afar for years yet he's never considered any of them truly an option for him. He's spent a lonely existence, only imagining the perfect romance but never coming close to it.
When Mike's drop-dead gorgeous friend Diane Hoffman quits her job after learning her boss and long-term boyfriend Robert Drake is married with children, Diane comes to work at the garage. Afraid she'll be weak if she relies on herself, she asks Mike if he'll help her convince Robert she's over him. Mike sees an opening to show Diane not all men are losers and creeps, unable or unwilling to be faithful to one special woman.
Diane is devastated about having unwittingly been "the other woman" for so many years and she'd determined to make a clean break from the unsatisfying relationship she's had with her lying, cheating beau. Though she's wallowed in her grief for far too long, packing on the pounds in her lonely misery, Mike is willing to help her put on a good show for Robert, who continues to pursue her. Diane has counted on Mikey's friendship for years but never really saw him as boyfriend material before, partly because of how overweight he'd always been.
But now Mike is fit and trim--and he's the perfect "pretend" boyfriend...so perfect, she can't help wondering if their amazingly sweet, sexy romantic relationship could last in the real world.