Igniting the Flame by Zoe Piper

Stu Johnson is a high-school English teacher who loves books, his cats and his single life. An occasional hook-up is more than enough for him. He doesn’t do relationships.
Firefighter Brett Parker is feeling left behind. His friends are settling down with partners, houses, and kids. His girlfriend dumped him eight months ago but he can’t muster any enthusiasm for dating or even hooking up.
When Brett has to leave his shared house, he moves in with his best friend of twenty years as a temporary measure. A candid conversation, some vivid dreams, and Brett starts looking Stu as more than just a friend.
Stu is more than happy to help Brett experiment and explore his curiosity. Neither of them are planning more than a bit of fun. But a slow burning ember can soon ignite a flame. Will they be able to keep things cool, or will they burn out of control?