*Spoiler* Helpful summary of the re-incarnation setup in Bpoop Phaeh Saniwaat

Kadesurang (eldest) and Karakade are twin souls. But due to bad karma which was not fully explained, it was the fate of one of the twins to die at infancy in each lifetime. In our Ayutthaya time, it was Kadesurang who died as a baby while Karakade lived, while in the modern lifetime it was Karakade who died as a baby while Kadesurang lived.

Por Date and Kadesurang are also destined soulmates so when Kadesurang died as a baby in the Ayutthaya lifetime, Por Date was basically mate-less for that entire lifetime. He and Kadesurang's twin never had a fated love which was why he never wanted to marry her. Por Date encouraging his father to chant the KrissanaKalee (moon mantra), caused Karakade's death. Although she deserved to die because of her evil deeds, it was still wrong for Por Date to be the one to play god and exercise judgement on her so his bad karma incurred in the Ayutthaya lifetime would come back and hit him in his later modern lifetime. Because he took away the life of someone, he was then destined to also lose his own soulmate in his next lifetime which is the modern one. Which was why his soul as Reungrit lost his own soulmate Kadesurang in that lifetime.

So, both Kadesurang and Por Date, although fated soulmates, did not have a fated destiny together for both lifetimes (Ayutthaya and modern).

What changed the situation was the following:-

1. Reungrit ordained as a monk for life and out of love for Kadesurang. This earned enough merit and good karma for them to then have a possibility of having a love destiny together.

2. Karakade also agreed to give Kadesurang her body so Kadesurang could then be re-incarnated again in the Ayutthaya lifetime and have the fated love destiny with her soulmate Por Date.

3. The KrissanaKalee mantra was the catalyst and route that connected the two.

Because all these 3 happened, Por Date and Kadesurang were able to have their love destiny together in the Ayutthaya lifetime, as opposed to none at all for both lifetimes. 

This is why the show is entitled "Bpoop Phaeh Suniwat" or "Love Destiny". It's about fated soulmates initially not able to have a fated love destiny together through 2 lifetimes but due to the great love and sacrifice of one of them which moved heaven and earth, they were eventually able to have a fated love destiny for at least one of those lifetimes.

Whether Kadesurang and Karakade are able to have a lifetime together as twins, we don't know. Karakade has a lot of bad karma to make up for. In fact, because she caused the death of a person and because of her very bad attitude in Ayutthaya that caused people to curse her name even after she died, she was not even allowed to re-incarnate and had to spend however-long in hell to pay for her bad deeds. Kadesurang, in Karakade's body, did a lot of good deeds and reversed a lot of the consequences which caused people to no longer curse Karakade's name and so won for Karakade a possibility of being re-incarnated again one day. But Karakade still needs to pay for her bad karma in hell because no matter how much good Kadesurang did for her sister, it still cannot completely erase all the bad karma incurred by Karakade (she took the life of someone after all). How long she needs to spend time in hell is anyone's guess but it has at least been reduced by her eldest sister's efforts.

This whole show has a large underlying theme of karmic retribution and fate woven into it. Actions always have consequences, whether in this life, or the next, because of karma.

But I was confused when Reungrit/ Por Date mentioned he loves Kadesurang since Ayutthaya since to me this meant,  Kadesurang was sent back for sure. So the fact that Por Date being mate-less in the original timeline was a bit hard for me to accept since Kade has implied that for us. And we know Por Date didn't and won't love karakade until Kadesurang inhabited the body which supported the "Por Date love Kade since Ayutthaya" theory. 

I believe better after reading your summary that it could've been like this:

Karakade dies after the chant of moon mantra. Kadesurang enters immediately after. She and Por Date have a lifetime together. 300 years later, Kadesurang and Por Date were born into the present era.  At age 25, Por Date's karma came back to bite him and Kadesurang dies. This leads to him ordaining for life to earn the merit that was able to bring Kadesurang to the past. (I wonder did he intent to bring her to the past or just that the merit and bhuppae sunniwat brought her to the past) And so, the cycle was complete. 

In that sense, Por Date was never mate-less. He was only mate-less until Karakade die.  I find this to fit in the "Por Date love Kade since Ayutthaya" theory which I noticed.

Though I find there are many loopholes in my own theory.

@MusicalVeggies

I did not know this drama was adapted from a novel. Thanks for sharing that bit.

I do agree with your theory on the scene I was talking about since it was also my other perspective of that scene as well. Though as you ended your reply, everything is but a speculation, we have no way of knowing how exactly the characters thought and what exactly happened nor did we receive a clear explanation on what happened. We could go miles talking about this and never find a clear answer. Though I do want to find the novel, is it under the same title?

Thank you for saving my confused soul as I begin to venture into this drama! 

I was confused with the ending. PorDat told her he would never take another wife, but in the last episode she’s putting the white garland in the little girls hair and there’s other kids with the white garland, so did he have sex with somebody else and they had babies. That completely ruined it for me.  If their love was destined, and pure, why did he have to sleep with other women?

What do you mean? I hope your explanation will help me. 

Thank you for the explanation, it made me feel a bit better. I thought maybe he had taken that Frenchman’s wife who actually was in love with him as like his concubine or second wife. I was confused because the service children who had the white garland flowers in their hair were considered to be the main house’s men children that they have with their servants. And then the little girl called him daddy. So I was confused. 

Por Date never had any other children with other women. The 4 children of his were all with Karakade (i.e. Kadesurang). In the last episode, both of them were even talking about the children - how the twin boys were Kadesurang's favourite and Por Date was even a little bit jealous because they were named after her 'old flame' back in her previous life i.e. Reungrit. The elder daughter was Mae Jumpa (Por Date's mother)'s favourite while Por Date's favourite child was their youngest daughter because she resembled Kadesurang the most with her cheeky and adorable personality.