I am sorry you are going through this. Relationships are full of little difficulties, confusions and scenarios. I know that it can be difficult to switch your mind off.
Sometimes we hear things that don't sit right with us. We sometimes hear things that we really don't want to hear. What helps me when that happens? I look at each conflict as a red flag.
A red flag is a good thing. It tells you to stop and listen.
In your scenario, you each have a red flag. For J, it's that he might not be doing an effective job of balancing his emotional output. Or, he might be taking on more than he can chew, in terms of his personality. Or, he might not be suited to one, or more, of his partner's personalities. He needs to listen to that and take some kind of action.
For you, the red flag is that you are potentially taking too much emotionally. It could be that you are taking a reasonable amount, but J isn't capable of giving you the care you need. Or, it could be that you take more than most. Either way, it is something that you can look at. The answer will be there in your gut; it will be there in your instinct.
There comes a point where we have to accept our partners, and ourselves, for the reality of who they are - their strengths, their limitations, the way that we are compatible, the way that we aren't.
I recently had a bit of an epiphany myself, thanks to the people here, about this kind of thing. There was a situation this autumn. I was so upset about my girlfriend's limitations. I couldn't get over it. Then, someone pointed out that I was missing something very important about the differences between myself and my GF. I realised that I had a realistic choice. Either accept her limitations and change my expectations - or leave/stay and be unhappy. Since I changed my expectations, expected something different from her, I can't explain how much it has helped.
Could any of this apply, with you and J? I've read your older posts and it often seems that you need more from him than he gives. At other times, it seems that you feel he has been patient. So, don't get me wrong - it doesn't sound like a bad relationship at all
But perhaps it would be wise to look at the differences between the two of you and alter your expectations slightly?
In terms of your specific scenario though -
No, it is absolutely NOT your fault. It is J's responsibility to speak up if he feels too stretched. But, like I said - why not turn this into something good, something constructive, and discuss your red flags?
As for shutting you out, I've been there. It completely and utterly sucks. I'm there right now. My GF is going through a breakup and we've gone from talking 5-8 hours on the phone a day to some days where she just isn't bothered about talking to me.
I'd say, give J some time to process. Perhaps tell him that when he's ready, you'd like to talk to him about what he's going through. Don't panic - things can feel horrendous one day, but be smooth again a few days later. Give him time to work out his emotions and that will increase the probability of him talking to you rationally.