Sounds complicated. I don't have much advice, except that if he says he isn't feeling well, maybe you should believe that.
And if someone is bad at communicating via text, stop texting. Communicate some other way.
it does sound like he's pulling away. i would definitely wait for him to contact you if you can stand it. him flaking on you is not a good sign but it is possible he just doesn't feel well at all and doesn't want to be a burden or needs some alone time. i wouldn't feel bad if he is not answering your texts right away. he could be busy or not in the mood to talk. some men will come to you for comfort when ill and some will not want to appear weak. it depends on the guy, maybe you have one of the latter. it could be that he is losing interest and is just making excuses as to why not to see you, but there is no use in worrying. whatever happens will happen. i suggest giving him some space and not get codependent on the guy and wait and see what happens.
Trust in your intuition. If you're an E, as you say you are, you will always try to seek other possibilities, which is ok and you're doing that. Are you going to be ok, if you are right about what is happening? Can you accept it and move on?
edit: keep yourself busy in the mean time until the guy can respond back on his own. Try not to stress yourself out too much, focus on yourself and look after yourself a bit too.
From my perspective as INTJ and someone with some chronic health issues, one of which is a sleeping disorder, I can say that it's very possible his cancelling of engagements and wanting to be home is due his illness/es. When I am very ill, I want to be in my bed. I want to just do my things, which usually involve reading books, watching something, or just sleeping. Having someone else there during that time is only comfortable for me much further into the relationship. This is not to necessarily say he is not retreating and rethinking, but it makes sense to me because I can relate to needing my own place and time. The best course of action in my opinion is to wait for him to contact you, while doing things for yourself in the meantime. It is not a good idea to 'sit by the phone'. Focusing on yourself and doing things you enjoy will give you clarity of mind and not allow the situation to control you.
If he contacts you and you make an engagement, meet up and have a meaningful and good time, proceed and see how things go. If he continues the same pattern, it would be reasonable to ask for a more direct answer to what's going on.
The way it reads to me is that you are up-playing your anxiety/needs and down-playing his chronic illness/needs. I think if you choose to be involved with someone with a chronic illness, it's implied you'll allow space in the relationship for it. I was cringing at the part where he tells you he's feeling sick and you tell him you're bummed (that you won't be having fun that night).
It looks to me like he's feeling/being pressured to downplay his illness, which isn't fair. Yes, he could have handled it better, been more direct, but it seems like he doesn't want to disappoint you. If you don't text him as usual after this spike in his illness you run the risk of looking like you are 'punishing' him for being ill (signaling either manipulation or disinterest if he doesn't turn up like clockwork).
As far as him not replying to your texts immediately during normal (healthy) times, that's a separate issue and standard INTJ stuff. I have an ENTP friend who gets agitated when I don't immediately reply to his texts, he feels ignored/disrespected etc -- that's all in his head. I like him just fine, clearly (I wouldn't be friends if I didn't), but my time is my own and I'm a busy person. I strongly recommend you don't take it personally. If you want to get a faster response, only text at times of the day when that's more likely.
Perhaps focus on the quality of communication rather than simply the quantity. Encourage open/honest/direct/'intimate' dialogue by making that comfortable -- be open/supportive/try to come to understandings with him (rather than all on your own like this). And be balanced. If you are going to talk about how you feel about texting make sure to hear how he feels about it too.
As far as that 'NF/NT death spiral' stuff goes; I have no idea why you're looking this stuff up at such an early stage in your budding relationship. Careful you aren't psyching yourself out. Since you have read it, I must say it was very NF sided. There are 'INTJ/ENFP horror stories' online that tell a very different story from the (bewildered) INTJ perspective.
If you think he's lying about his illness in some way, then you have really big problems in this relationship. Whether it turns out that he's a liar or you have serious trust issues -- clearly one of you is not up to standard and this relationship will end, one way or another.
If I were you I'd be open/responsive and stay calm while I let him show me what he's about and what he can realistically offer (especially with his chronic illness). INTJs respond well to direct language with no pressure. Make him aware of your needs/expectations. If it turns out you don't like what he can offer, decline it and go meet someone else.
Last night after he told me that he's not feeling well and wants to be at home,
I said I was bummed that we couldn't get together but that I hope he feels better.
He apologized then and said he was going home to take his meds to try and beat it, to which I replied "you are totally fine, I'd rather you get rest and feel better. I mentioned that I thought I was coming down with a cold...and that I hope we both feel better by the weekend. He said...'I really hope so...I haven't felt this bad in a while'
I replied I'm sorry you're feeling so bad...if there's anything I can do let me know.'
The last message was delivered but has not yet been read..and I have not received a text today as of yet.
I know that he is truly ill... and I don't want to bother him as I know he needs his own time to recoup.
I will busy myself with other things until I hear from him...but I don't want to...as you said..'run the risk of looking like I am punishing him for being ill...by signaling disinterest.'...from not messaging him.
@erinkaciebrown, don't punish yourself. If you want to communicate and keep trying, then do that. Be you. If he doesn't like it then well that's his problem. I don't think you're doing anything over the top.
Why do I keep missing the full posts when these things go up? It's ridiculously intriguing. Anyway, I can't speak for him, but speaking for myself, I like to keep people aware of what I need/want. Occasionally I need to tell my INTP that I need some "me time". I tend to give him an approximation of how long I need (hours, days, a week, etc...) and why (overwhelmed at work, haven't been reading enough, need more time to think, etc...).
What I say is what I mean in these situations. I don't have many problems with upsetting my current partner, but previous boyfriends weren't very understanding of just how much time I needed by myself - even my more introverted boyfriends.
For me, I don't pull away; I tell someone directly that it's not working. In my mind, I would like it best if others are direct with me, so I'm direct with them.
While I have no idea what your original post said, definitely don't blame yourself for his needing space. And if he is pulling away and doesn't have the respect to tell you in a direct way, then you can do way way better.