Mycroft and Lestrade have always had bad timing. Lestrade and Mycroft have been in and out of each others lives. Misunderstandings and class issues keep them apart, but they always seem to find their way back.
Lestrade leaves his wife after she admits to having an affair. He leans on Mycroft and eventually uses him as a friend with benefits. Mycroft has always had strong feelings for Lestrade but goes along with it no matter how much it hurts him to do so.
