Lesley isn't quite good with other people when he doesn't have the goal to kill them in the end in mind, he hardly talks and avoids contact so it would be quite hard to get him out of his shell. Man just wants to go back to his rats, dog, garden and computer after work ! Though if you like any of those and aren't too hyper around him that could be a good angle to start with.

Elov managed by being ambiguously suicidal enough to confuse Lesley into letting him live long enough to brute force himself into a "relationship" (but you have to be brash enough and well, kind of dangerous enough to survive the first attempt) and Wallace wormed his way in by being forced in Lesley's care and moping around enough that even Lesley would offer to share time together to stop it (that's complicated because you'd need a twink with enough charisma and leverage to convince Lesley not to kill you)

So hum. You'd need a loooooot of time and patience and a knack for rodents and/or early personal computers. Good luck !