Why did God join you together, and why did the marriage fail?
I'm a very open and honest man, so I'm definitely not trying to evade the first part of this question. It's just that there are so many different variables involved in the correct answer to this question that it might literally take me a lifetime to properly answer this. If I had to try to sum it up in a short statement, then I'd say that God is much more concerned about our eternal destinies than he is about us experiencing a "comfortable ride" during this temporal life. In other words, in order to properly prepare us for eternity, God will oftentimes need to deal directly and even severely with our hearts. Sometimes those dealings will come in the form of healings and deliverances, and other times those dealings will come in the form of rebukes and corrections. Without going into any specific details at the moment, I can honestly say that God sought to deal with both me and my ex in both of these areas on a daily basis in order to properly prepare us for the world to come.
At my end, there were some areas of both sin and inner wounds that weren't fully dealt with in my life until God REALLY turned up the heat. The Bible calls such things "fiery trials", and, like gold that is purified in the fire, God exposed a lot of dross in my life/heart through what I experienced in my marriage. BELIEVE ME, my trials were EXCEEDINGLY HOT...to the point that I literally despaired of life at times. In fact, I recall driving alone in my car one day on the highway while sticking my head out the driver's side window, looking up towards heaven, and literally screaming "ENOUGH!!!"
They say "If you can't stand the heat, then get out of the kitchen". Thankfully, I stayed in my fiery trial until the time came that God had removed the dross that needed to be dealt with, and until the time came that my ex ultimately cheated on me repeatedly and then divorced me. I'm a much better man now than I was when I first entered into my marriage covenant, and, as fiery as my trials were, God never released me from the same until the time came that my ex cheated on me and divorced me herself. There are a lot of people, including some people on this very website (based upon their own testimonies that I've read) who seem to believe that there are a host of different acceptable reasons to procure a divorce, but I vehemently disagree. Anyhow, divorce isn't the topic being discussed here, but I felt the need to just mention that anyway.
To this part of your question, I would also add that my marriage affected a lot of other people's lives as well that God wanted to do works in. I could greatly elaborate on this point while giving many different precise examples, but I won't. Of course, my marriage also resulted in three precious children being born, so there's their lives to consider as well.
Marriage isn't just about snuggling on a sofa while sipping hot chocolate and watching a Hallmark movie. If anybody wants a realistic view of marriage, then I would heartily recommend that they just read their Bibles from cover to cover. In other words, as I've rightly stated many times on this website before, God's covenant with his people is likened to a marriage covenant all throughout scripture. If anyone reading this thinks that THAT "marriage" was/is all fun and games, then I honestly question their sanity. Marriage is messy, and it's definitely not for the weak-minded. I'm NOT trying to make it sound like all gloom and doom because it isn't, but it's no day at the beach either...unless we're talking about a scene from the movie "Jaws"...lol.
Why did God join you together, and why did the marriage fail?
This part of your question is much easier to answer.
Ultimately, my marriage failed because, despite all of the healings and deliverances which God had wrought in my ex's life, she ultimately didn't want to live the type of self-sacrificing Christian life that Christ calls each and every one of us to. It was NEVER an issue of me telling her things to do that she didn't want to do. Instead, it was definitely and always an issue of her not wanting to do the things that God himself was showing her to do.
There were many times throughout our marriage that my ex came to me and told me of either a dream, or vision, or word that the Lord (not me) had given her. On every such occasion, I knew that it was the Lord himself who had told her or shown her the things that she was hearing or seeing. It simply wasn't what she wanted, and she ultimately renounced Christ/Christianity while trying to destroy me continually throughout the ongoing process. In other words, rather than just be honest with the Christian community that we were then a part of, my ex sought to demonize me continually (as in multiple times every single day for many years) as one who was guilty of both domestic violence and multiple accounts of child abuse. In fact, she ultimately pressed such phony charges against me in a court of law, and I needed to appear in court to defend myself. I was found to be totally innocent of the charges, but my ex ultimately got what she wanted. In other words, the gullible/undiscerning "church", including more than one "pastor" (read: HIRELING), helped her tremendously during that whole ordeal (she fleeced them for all sorts of monies and other material goods) while they all shunned me as if I was Satan himself.
Anyhow, as crazy as this sounds, my ex actually cooked me dinner last night...so go figure. There's definitely no chance of reconciliation between the two of us, but we're quite amicable now (as in now that she got everything that she truly desired), and I still pray for her daily. Her home is littered with all sorts of idols, and she's into all sorts of Eastern demonically-inspired religions, and she regularly takes Jesus' name in vain now. It's horrifying to watch, but she has her own free will.
I'm still trying to reach my own children who were caught up in this whole mess and greatly turned away from Christ/Christianity (especially my two daugthers...my son wasn't as swayed as his sisters were) in the process. Just last night, I had the privilege to speak to one of my daughters for about 30 minutes on her necessity to receive Christ as her own Lord and Savior. BELIEVE ME, while we were still living together as a family, I taught my children on every topic imaginable from the Bible, so they're no rookies when it comes to knowledge of the same. Anyhow, I'd rate our conversation last night somewhere around the 50/50 mark. In other words, there were some things that I shared with my daughter that she agreed with and others that she vehemently rejected. As I said before, marriage is no joke...especially if children are involved.
I hope that this somewhat answered your questions.