Hi Tracy! I love Burn Notice, too.

Proverbs 27:17: “As iron sharpens iron, so must one man sharpen another.”
[FYI - this is my interpretation of this passage from a literary bent, and is not intended to be a religious discussion per se...]
There’s lots of examples of how things become sharper, more refined in the Bible (refinement of metal through fire; separating the wheat from the chaff, crushing grapes to remove the skins, leaving only what is needed to make the wine, etc; in this instance, the symbolic image of two pieces of iron slamming against one another, which makes it stronger/tougher). It’s about needing a person in your life who is going to tell you the truth, whom you can trust, whose opinion you respect. It’s about being in the presence of someone who loves you - a person of integrity, strength, and courage of character - and how the interdependence between you both makes *both* of you stronger, wiser, more directed and confident in where you’re going. It’s a mutual “give and take” kind of thing. This is how I see it, anyway.
This is what I think what Michael was trying to say - that there is never going to be a time in his life where he isn’t going to need her on that core level. Because she makes him a better person; because he respects and values her opinions; because he can trust her to tell him the truth. And because they have a remarkable history and have shared life-threatening experiences that very few of us could ever begin to understand. And that's why there is an interdependency between Michael and Fiona: they sharpen/strengthen one another. I think it was Michael’s way of telling Fiona that he wanted to be there for her, the same way she’s been there for him.