Hi! i don’t think this is a bonding question, or rather it’s like a mixed bonding and health-care question.
It’s always worrisome when a bun starts to eat less. It’s very good that he still takes treat though, because a really sick bun won’t take a treat and that’s when it’s about to become an emergency.
Bonding is stressful to rabbits, not necessarily in a very bad way, but it is upsetting to their system. All forms of stress have some impact on their gut. Not wanting to eat hay and healthy stuff could lead to gut slowdown. From that, he could get gas, that’s very common and gas is painful for a bunny. According to Medirabbit you can give baby gas drops (simethicone) on suspicion of gas, it’s bunny safe. I always keep baby gas drops at home for this reason. There’s no hard scientific evidence that it actually helps, but it’s harmless and many bunny-owner (f ex I) swear by it.
Junk in rabbit food can be fine for a young bun who is growing and energetic, but not good for an adult bun, so his getting to be a mature bun could mean he doesn’t tolerate the “junk” like he used to. I’m sure you know that dried fruits etc are bad for bunnies, so I won’t lecture you on that =) but I do think it would be a good idea to try and very slowly taper out the junky mix and replace it with plain good quality pellets. This needs to be done over a month or even longer, rabbits don’t tolerate rapid food changes very well.
The mainstay of a bun’s diet is hay though, so his not eating hay is a problem. Sometimes it’s the hay, f ex a new batch of hay that has a different texture than the type the bun likes. They can be quite picky with hay. Sometimes it’s the bunny’s teeth, especially the molars. They grind their food with their molars and that’s important for dental wear. Buns can develop molar spurs that makes grinding tough food painful, so they stop eating hay. This in turn results in the molars being worn less and the spurs can grow even more (vicious circle). The gut doesn’t get enough fiber, which makes it work less well. This can lead to gas or sticky poop or very very small poop and in the longer run even GI stasis. If this goes on, you should have your vet check his molars.
These are just a few of my thoughts, but it could perhaps be a starting point. If you get his food/tummy-issues sorted, your chances of bonding your buns will be greater – well obviously. There are limits to how charmful you feel when you’re having tummy trouble, that goes for humans as well as rabbits.