He is still being affectionate; he is just finding his own comfort zone. Really, each cat is different. I have two kittens and an adult cat and the two kittens are now as different as any two people. One will let me cradle him in my arms like a baby, the other doesn't like to be held that way. One lays near my head when he wants attention the other doesn't do that anymore. But they are both affectionate.
Cats need to deal with their own nervous system. Some cats cannot tolerate a lot of petting. More than one stroke and their tail is twitching. It's not that they don't like it; it's more that their physical bodies have tolerance levels and these vary from cat to cat.
When my kittens get bored (and they do look bored often but I don't worry too much about it) I rip a piece of clean white paper, crumple it up into a ball...while I'm doing this they are both getting ready for the fun they know is about to come...then I throw it onto the kitchen floor and watch them both go chasing after it. The paper makes a neatO noise and it is small enough to bat around and bite and carry from place to place.
Later I go around and throw the old paper balls away. I don't let them play with them more than half a day, a day at most.
Oh, the caps from water bottles are also great-sounding fun toys for kittens.
Come to think of it, in five months, I've bought NO cat toys for my two kittens. They find enough to do. Boxes: every time a new box comes into the house I treat it like it's the biggest deal since Meaty Morsels. With grocery bags you have to watch them though, kittens can get caught in them.
I think one of the funnest toys I've had around is a stick with a medium weight string, to dangle it for them to chase. At the end of the string, tie a piece of lightweight yarn about 8 inches or so. Then, when you move the string around the yarn on the end looks like a real bug. My older cat loves that one.
Also, when you feed your kitten treats, use this time as play time too. The vet gave me some samples of healthy treats for the kittens. They are like dry food so when I give them I toss them onto the floor and have the kittens HUNT them. I scatter them maybe three feet in diameter across the floor and this keeps them occupied for at least five minutes or more.
Before you go to work, hide treats near your kitten's favorite hangout windows. As you notice he has been finding them, hide them in more difficult locations. As he grows this will become a satisfying "game" for him, and it will keep him busy and always on the lookout for his food, the hunting instinct.
Also, do little things with your eyes. When you are sitting on the sofa and your cat is on the floor, if he looks at you, do this: look at him, look at the sofa where you are sitting, look at him, look at the sofa. Sort of inviting him up with you with your eyes. I do this and I swear my cats completely understand and jump up with me just about every time.
My kittens are also going through a calmer, maybe a little restless, period now. They are about five months old. They do have each other but I am starting to think of building my cat tree and even an outdoor enclosure for them. So I know what you mean.
Don't be too hard on yourself. I think people feel guilty. Your kitten will adjust. Just be sure to play with him.