Eliwood's experiences re: girlfriend, father, etc left him deeply messed up and either a basket case if Ninian leaves him again or a pretty wounded individual if she stays as a daily reminder of the killing and such.

I think I can see the basis for that argument, yeah, but I don't think I could subscribe to it fully--Eliwood's definitely one of the most level-headed and saner lords presented in the game. (Though now that I think on it, all his experiences would definitely take their toll on him.)

There's a lot of things about Lyn that are messed up, but I don't know if I would go so far to say that she's more messed up than Eliwood.