I believe that there are many people who could be suitable for us (not just one) that God would want us to be with. God would want the BEST for us rather than people we sometimes choose ourselves (that may not be according to His will). What you are referring to is soul mates. I have read so many articles on soul mates. Soul mates are partners who are spiritually mature. From what I read, it is a relationship based on *spiritual* attraction, not physical attraction. So that to me means that there is a major difference between godly marriages versus man-made marriages. Bottom line: if it was up to God, God would match us up with people that are the BEST for us...just like a parent who would want the BEST for his/her child.
But to your question, I think some marriages don't work because it could be due to many reasons: spiritual immaturity, incompatibility, settling for less (not waiting for the BEST), not putting God and marriage first, hardness of the heart, etc. It's hard to lump divorce into one category because every relationship is different. Good thought-provoking post!