Have you been able to get close enough to him to check him over? Make sure he hasn't got anything physically wrong, as cat's will try very hard to conceal any sign of weakness/illness. Might be worth just giving him a gentle physical to make sure he doesnt have any wounds or bites you're not aware of. I'm sure he won't have, but it's worth looking.
It might be that he's wary of upsetting Ellie generally, and so has become more reserved as a result. On the other hand, he may be feeling a bit more confident about his surroundings, so less need to have as much reassurance - being around him you'll know which it's more likely to be.
I think I would make a point of seekinghim out when he's having some "alone" time, and just gently instigating a little affectionate touch. Maybe just using a closed hand to stroke him, and not overdoing it. One touch is enough to let a cat know that you're thinking of him/her - even just popping your head into a room they're in and saying "Hi" counts to a cat. They don't always welcome being handled or picked up, although as you say, Eddie was more free with his affection before, so might welcome a little time alone with you.
Tinks is very wary of affection - he hates being picked up, he never sits on a lap etc, but he does love it if you go up to him when he's on his own, and give the base of his tail a little scritch, or behind his ears. He gets a big silly grin on his face and purrs like crazy, but often gets overcome with his own daring and scampers off looking embarrassed, yet hugely pleased with himself.
Last night for example, I got up in the middle of the night, and he was lying on the floor next to the blanket box. When I came back to bed, I gently picked him up and popped him on the bottom of the bed. he at once snuggled down and lay across my foot, but sometimes he needs that little bit of encouragement. And sometimes he just won't countenance any kind of proximity. We know he loves us just the same, so we can afford to give him the space he needs when he wants it.
I wonder if Eddie is maybe feeling the same? Tinks wasnt always our cat (like Eddie hasnt always been your cat) and even though he moved in with us as a consequence of his being our then cat's best buddy, he's very much "lead cat" in our house in terms of the fact that Moray joined us after Tinks arrival. However, Moray's very definitely "in charge" and I wonder if that's how it is with Eddie and Ellie?
Just a few thoughts to ponder.
The main thing is, they seem to be tolerating each other's space pretty well. Possibly the price that will be paid for that is Eddie being less friendly. When we had Paddy, we introduced a kitten when he was two years old. Paddy became more distant too. He tolerated the interloper, but he spent much more time outside, and was far less affectionate with us than he'd previously been. When we lost Flynn, Paddy became much friendlier again, although he was never what you'd call a lap cat, bless his heart - he just liked to know we were there if he needed us.
It wasnt until the last 5 years of his life, and following a stroke, that he would seek us out, and sit next to us. That was more for reassurance, as his stroke left him deaf and somewhat disorientated for a time.
Cats are complex creatures, are they not? The best we can do is observe and learn their o wn preferences, habits and charateristics, and try to ease things along where we can. You're already doing that.
