Unless he's had nothing to do while sitting in jail but to plan how to get of of there
This is how I see it, as well.
He's been trouble all his adult life, while Vicky allegedly has always been upstanding. Something made her crack, or maybe she hasn't been as wholesome as she appeared until now.
There has to be a motivation for each of them. People do wild things when they see the reward as worth the risk.
IMO his motivation is dual: he wants to be out of jail or prison. Also, I believe that the powerful emotion guiding him is his stated desire to kill his ex-girlfriend if he gets out of jail. I think he did sit around while locked up, pondering how he can get out to achieve this goal that consumes him.
Then he sees this single, middle-aged, female corrections officer around. Well, he's a con artist who hasn't hesitated to hurt people in the past. Maybe she seems to be looking at him a lot, maybe not, but somewhere along the way he caught on that she could be manipulated with some male attention. So he gives it to her. But to him she's just a conduit to his escape.
Her motivation had to also overwhelm her enough to make her throw aside everything she knew to pursue a future with CW. He must have persuaded her that they'd live happily ever after once she got him out into the world.
If before the jailbreak they have had a "romantic" but not sexual relationship, then she may have been dreaming of life with him where they could consummate their relationship. If they DID have some broom closet encounters, how did they manage that with cameras all around? ( I ask rhetorically; we can see how lax security procedures were at that jail).
It's pitiful that he manipulated her enough to facilitate what I see as a desire to kill the ex-girlfriend, and to get out of jail free.
But I have no respect for a senior corrections officer who could allow herself to be so manipulated.
For her mother's sake, and for her nephew's sake (so she must have a sibling, after all) I hope he hasn't already finished Vicky off.
Jmo
ETA: as to the aspect of him blackmailing her, how would that be possible unless she was already sidling up to him somehow? That would suggest she confided her darkest secrets to this prisoner. If she had done something that was known by others, he couldn't have blackmailed her since whatever she'd done was already known. Hence she would have had to share it with him and him alone. Which would already have been very, very stupid on her part.