Having had one failed marriage myself, I firmly believe that the thing that was lacking was communication.
If you can't talk about everything, good, bad and indifferent, then any love that is there is likely to fade over time as there's nothing there to stoke it.

I realise now that in my past relationship we BOTH took each other for granted. I'm not going to let that happen again, and even though my currnet relationship is long distance, and english not her first language, we communicate more now than I ever did with my ex.