Well, I for one, wish them the very best of luck. As a person who has been married 3 times, I know how easy it is to make mistakes when you are younger but learn from them so that your 3rd marriage is actually a success. Reading all the comments on here make me think that instead of feeling very happy that I have actually managed to make a success of a relationship, I should hang my head in shame as I married my third husband in white, in a church and my DH was an adulterous divorcee too.
Most of the people who came up against church rules which precluded divorcees getting their vows heard in church, experienced this many years ago when things were very different. The age when pregnant unmarried mothers were forced to give up their babies for adoption. The fact that society has changed enormously, allows Boris and the rest of society to marry in church, catholic or not, so the rules have not been changed for him. The only difference for most of us is if your Parish Priest chooses not to allow this to happen because they still hold a lot of the power over these matters.
If you read about the childhood of the Johnson children, there are lots of red flags about their development. They moved home a lot, they were largely brought up by au pairs, pushed to be high achievers and experienced parental depression. Boris himself suffered with deafness and had several operations which in the days he had his treatments would have likely left him without a parental presence as that was quite acceptable then. If you read the statistical evidence about Boarding School children, forces children who move around a lot and children from families who haven't been brought up with a strong parental bond (particularly with their mothers) divorce and difficulty with relationships is much higher than those with stable childhoods.
Whilst it doesn't excuse his behaviour within his previous relationships, it might explain it and surely we can have some compassion on what is supposed to be a happy occasion for the couple. Maybe Carrie will be the one who can help him with a successful relationship. After all, we only have the Media and a poisonous little toad's view of their relationship so we all know how reliable that is.