How long has he had the fissure?
With respect, what you will have read about how painful they are is based on the least severe end of the spectrum. If it hasn't healed then it will be at the more severe end - and those that don't heal by themselves usually require surgery and are f*cking agonising. I say this from personal experience. I needed surgery, opioid painkillers to keep the pain under control, and obviously had to be signed off work. The NHS info, if that's what you read, about anal fissures is so far removed from my experience and the experience of people I've talked to that it's almost laughable.
Equally, inconclusive camera tests do not equal nothing to worry about, other than they haven't found cancer. Inflammatory bowel disease can be missed in biopsies if they're not taken from an inflamed point or during a bout of inflammation, and some bowel issues like bile acid malabsorption or SIBO can't be found by a camera test, they require different tests.
My camera tests were inconclusive, I was told it was just anxiety, and then I ended up nearly dying and needing major surgery. It was not "nothing", it just wasn't picked up by the tests they did at the time they did them.
Bowel disease, if that is what is going on, can cause malnutrition and fatigue, because the body can't absorb what it needs regardless of diet. Also, if he does actually have an inflammatory disease fresh fruit and vegetables would make it much worse, whereas processed food would make his symptoms better.
Whilst it's lovely for you that you're able to get on with things, as you've apparently told him, you are not him and you are not experiencing the things he is and has. None of us knows what it is like to walk in another person's shoes, even if we think we empathise. It's unfair and unhelpful to tell people "well I have problems and get on with it". You are a different person. Just because you can cope with the problems you have, doesn't mean he can cope with the different problems he has.
Incidentally, trauma, especially the kind of trauma of suddenly losing your family in the way you've described him losing them, can manifest physically in the body for decades to come. Often with the kind of symptoms you describe. It's not "in his head" if that is the case, it's that the body gets stuck in a hyper alert state, which can cause inflammation and in turn physical illness.
Sometimes people don't push for more tests because they're scared of what the results will be. Or scared that they'll put themselves through the extra tests and still be left with no answers. That can be worse sometimes, when you're living with the physical effects of something being wrong with your body, but being told that because they can't find anything it must be in your head. Modern medicine is still a lot of guesswork.
Propranolol for anxiety, either works instantly or not at all. It only takes away the physical symptoms of heart racing etc, it wouldn't fix anything else anxiety related. It might help people push past anxiety fears and interact with people for instance, but it wouldn't calm your system or your mind necessarily. It's a bit of an odd thing to prescribe on its own as a first attempt. I've only seen it provided as a supplement to proper anxiety medication.
All of that said - if you can't live like this, you can't live like this. I don't know him, I don't know what it's like to live with him. If his health remains like this, will you be able to cope with this being your life without taking it out on him or becoming desperately unhappy yourself?
My impression - and that's all it is - is that there are swathes of this where you have been quite harsh and unfair, but also elements that sound like he is possibly being manipulative. Whether that's taking advantage of the situation or something else, I don't know.
I am puzzled what you mean by him complaining you waste his time if you go out without him? How does that work?
Your comments about things like that are a bit concerning.