When you say 'there are some children you will never like' . . . I'm afraid that that's where I think I am.
But do you know why?
You say you've done a lot for him, but kids will always value much higher you attention and esteem, even though this is often an unconscious feeling even at an early age, then the material things you get them.
Take two managers. One has got you a nice office, nice furniture, a good salary and a company car, but they never show you warmth, shows no interest on how you get on with your job, doesn't want to know about your personal life, is polite and courteous, but you can tell that they don't really like you.
Other manager tells you that unfortunately, they can't give you a nice office and you might need to share for some time and furniture is used because they couldn't afford new ones. They can't give you a company car. However, they are always stopping in your office for a talk, tells you to approach them if you need any help with any aspect of your work, ask about your family and tells you that you can work from home if you ever need and tells you that you do a fantastic job that is vastly contributing to the success of the company and that they would really struggle without you.
Which boss would you rather report to and make you want to come to work?
I think his analogy is quite similar to how SCs feel when they go to see their dad. I expect your SS does know perfectly how you feel about it, or if he doesn't yet, he will soon as will your DP and will most likely get to the point where you mostly ignore each other. It works with some family, it doesn't for others.