I think there are many many marriages like this. I don't see why you would leave right now if you are essentially amicable and you are happy to wait til the children finish schooling. Everyone saying- well, they will feel bad because of XYZ, my own experience is that many children find divorce and their parents separating at any age a difficult experience, but equally most just want their parents to be happy- I was very happy when my parents divorced after I'd left home and gone to uni as I was out of the way for the whole messy business but they were separated which was good for both of them. The idea it would all just go really nicely if you divorced right now is also a false hope.
If you are not hostile, aggressive or rude to each other, you are actually going quite a lot better than many married couples.
I don't have a massive problem with this at all, relationships come in multiple forms, I think your children will see you have outgrown the arranged marriage, but also may be thankful you kept stability during secondary- being a new girl or boy in say the second or third year of secondary where you know no-one is disruptive and disturbing whatever posters say- my kids have taken a year to settle down after a school move.
I don't believe there's a right answer, and of course in an ideal world, you model love, kindness, tenderness and so on, but in the real world, many marriages are a compromise (over sex, work, priorities, arguing styles) and yours is no exception. I think it is over-egging the pudding to assume this is 'damaging' to the children especially when you seem on good terms with your older children and can speak honestly with them.