...in order to have spent years in long term relationships with women, fathered children, gone to family weddings, even going to relationship counselling just to make their cover stories more plausible?
Seriously, normal people with normal emotions just wouldn't be able to do this 
www.guardian.co.uk/uk/2013/mar/01/police-spy-fictional-character?INTCMP=SRCH
"At one stage, he is known to have attended counselling to repair his relationship with his wife. Bizarrely, at about the same time, he was also consulting a second relationship counsellor with Alison.
"I met him when I was 29," she said. "It was the time when I wanted to have children, and for the last 18 months of our relationship he went to relationship counselling with me about the fact that I wanted children and he did not."
www.guardian.co.uk/uk/2013/jan/17/spies-sexual-relations-activists-routine
"In two cases, women who were sleeping unknowingly with undercover police officers invited the men to the funerals of relatives. Police spies shared homes with the women they spied upon, met their families, told the activists they loved them and spent weeks and even months travelling with them on holidays abroad."