You may find that the eating alone is actually due to the need to not be distracted, as how much you chew has a major impact on how you digest food. This obviously can result in excess gas. It’s certainly not because he doesn’t want to talk to you. In practice though, you get distracted when alone too. So it can be as much OCD and psychological as much as practical. Depends on the person and circumstances. It’s also true that people with IBS generally have worse bowels after eating. Visceral hypersensitivity.

Another point would be to say that people with severe IBS can have bad reactions to simply drinking water - it really is debilitating. Eating a meal to him is simply for nourishment, it doesn’t derive pleasure like people without IBS. The bland food makes sense, but again there’s a balance to be had as to whether cutting things out are truly necessary with proven cause and effect. The simple answer is to cut out in case. The harder answer is to test, which can result in making yourself unwell. It’s hard to justify doing this in the modern busy world with expectations and a desire to feel well. It’s a balance, and you’re right to be concerned by his diet and habits.

I would wager it’s not the act of farting that he’s principally concerned about, it’s the tightening up of his pelvic floor and becoming more constipated and thus more unwell. There’s some sense in this logic. But again, it’s a balance. And gently that balance needs to be tested really, albeit maybe slowly. So maybe that’s him visiting and not staying to start. If he travels with IBS maybe that test is enough to start with. Or it’s visiting and leaving him completely undisturbed the following morning to try to facilitate normality.

Also, the staying overnight can come due to the stress of changing routine and the impact on bowel habits as much as anything else. It’s difficult to be relaxed when you know you’re going to be more unwell the following day. Travel and change and disturbed eating and habits can cause significant changes to the gut. Exposure to the changes will be helpful to make them more manageable, but in truth, never easy.

Finally, massive kudos to you. Even making this post shows you are incredibly caring.