Hi cavlover welcome to the forum.
I am very new to the fur child raising, I have a little 11mth old cav whom I love dearly, We are still going through the toileting thing, although he has been much better as of late. At night he will use a puppy pad as he doesn't have outside access once we are all asleep. During the day whilst we are at work he is gated in our larger bathroom and I am able to scoot home for toileting early afternoon. I am finding that he waits until I come home to toilet outside as his puppy mat is dry.
I find that he likes to mark my daughters bedroom, so he is only allowed in there when we wake her and he is supervised. Otherwise the door remains closed, if by accident it is left open he is quickly called out of there, but alas we still have the occasional lift of the leg in this room.
When we visit other people's places he does do the marking thing as well. He has been desexed but boy he likes to lift his leg. So the majority of the time we are visiting he spends on my lap unless we are having coffee outside.
The other thing was he did have an aversion to pooing on the puppy pad but he has recently started to do this. I have my fingers crossed he continues to do this.
One day it will click, until then it is extra vigilance and clean up messes, and lots of praise when he gets it right. It sounds like your little fellow misses you. I am sorry about your constant re-training but all I can say is that I believe it will get better with time and consistency. Maybe someone else with more experience on this forum will be able to advise you more or let you know different training tactics that have worked for them.
Would love to see pics of your little angel.