Why did apple filling in the pie turn to mush?
Hold back a bit on the lemon, or toss 1/2 teaspoon of baking soda in the filling. I don't see any other cause for the apples to have completely macerated in your recipe other than the acid content to cooking time. 90 minutes is a rather long time, but I'd expect them to hold up quite a bit better than 'mush'.

You could also try blind baking your bottom crust for 15 or so minutes so the final cooking time is shortened, which presents less opportunity for the apples to soften. Ideally, you want to be in the 45 minute to one hour range. 

If it were me, I'd probably try both. Keep trying and experimenting, bringing a fresh pie to the table is one of the most satisfying ways to delight your friends and family :)