I know he said I love you to his mom a couple times but I never remembering him saying it to Fiona. I know it makes sense a bit with their characters being no good at relationships but I was expecting it to happen in one of the season finales.
Michael's got issues...he's emotionally scarred by "love"...he can't say it easily, he shows it...and Fiona knows that. During their prison visit, when he's trying so hard not to break down and tells her he's going to get her out, she says, "I love you too, Michael".
Fiona understands that for Michael, actions equal love, so that's why she gets so upset when she feels his actions are not in line with his love for her. That's when she questions whether he loves her enough. She always overreacts when she doubts it.
Perfect example. Remember the morning after the fire when Michael thought Fiona had been killed? He went out and got her that no-egg-white omelette? Came back to the loft and she was gone. He was so hurt by her disappearance. Getting her breakfast was his expression of love. Not words.
Building the shelf for her snow globes was telling her he loved her. Helping her with her bail bounties, even when he didn't want to.
I think in "The 5 Love Languages" that's the language called "acts of service". :)
I'm always amazed at Matt Nix. Is he really that well rounded in psychology or is it just luck and intuition that allows him to make his characters (especially male) behave so true to form? He must truly be a great observer of people. Or maybe he fanatically reads a lot about people and what motivates them. If so I can relate. :)