Sure, it was a surprise. Not a big surprise, but a suprise. The cold shoulder when Greg mentioned love, the almost robotic like actions. But the killing was what really gave it away. It had been the middle of the night when a man broke in and tied Greg up. Mycroft had shot him easily. No remorse. No guilt. Just the calculating look he got on his face when he was thinking. That's when Greg knew.
The only surprise was Mycrofts tears when he brought it up. He sobbed that Greg would leave him if he knew. So, Greg stayed. Mycroft explained to him the situation:
"You are a good person, a great lover, an amazing friend," Mycroft murmured. "I don't love you. But, finding someone else as high quality as you would be a hassle."
Greg figured that was the closest thing to a love note that he would ever get.
And, life went on. Greg was more careful around Mycroft after the incident. He wouldn't anger Mycroft or annoy him for fear of his boyfriend loosing control. After a while, it just seemed normal to live life without love. Mycroft would leave him alone for weeks and then show up one day with flowers. He would kill the parking attendant that gave Greg a ticket and send him the fingers.
On their wedding day, Mycroft cried.
"How could I find someone as perfect as you?"
It pained Greg to know Mycroft wasn't talking about love. He was talking about their compatibility. That Greg put up with him and shagged him every couple nights.

But, then again, isn't that what love is?