Sounds like a positive meeting with the GP and hope he gets his results ASAP and referred to the right specialist.
I was diagnosed with Colitis around 8 years ago. I had to fight hard to get listened to even after I was referred to the specialists. My blood markers never really showed inflammation even though I'd be losing lots of blood, losing weight and going to the toilet 30+ times a day. Eventually they done stool sample which showed really high levels and now they always do stool samples on me as well as bloods.
I also had a lot of hosp appts cancelled so wasn't seen for over a year whilst I was suffering and medication lot working. In the end I made a complaint to PALS and things got a lot better after that. My care is great now and I feel very looked after and listened too.
You sound very supportive, he's lucky.
It's hard to offer advice as IBD effects everyone differently and medications work for some people and not others. If he does show inflammation they will probably send him for a colonoscopy so they can see and also take biopsies of the bowel tissue to determine what type of IBD it is. Getting him in his favourite food after this procedure will be a nice gesture as he will be starving.
The CCUK website is really helpful as well as their private forum on Facebook of you are on that. It's good for asking questions, it was a saviour to me when I was first diagnosed.
It can be a very isolating disease in lots of ways, anxiety as a result of the symptoms is very common too.
If he gets achy joints running him a nice hot bath is a nice thing to do. I love it when my BF runs me one when he knows I'm struggling.
You could order him a radar key off of eBay - helps when you're out and about and need the toilet quickly.
But yeah, I would just say don't give up and make sure he keeps pushing.