How come it's so hard to accept that this quality time with him just can't be the same as it is with my other partner? How do I start appreciating more this different kind of time spent with him?
You get a pencil and paper and you write 5000 times:
"I will appreciate the quality time spent with him even though it can't be the same as it is with my other partner."
Seriously. You smack yourself with a clue-by-four, pull up the big-girl diapers, and just do it. It doesn't have to happen over night. But you basically answered your own question.
Or as Yoda would say: "Just DO. There is no 'try'."