I'd like to welcome oyu here to the Forum. As someone else that has anxiety I can relate to what you are going through however I'm not sure you are on the right track.
You had a lot of contact with this person in the past, but for whatever reason he indicated he did not want to continue. Despite all your attempts at contact he has not replied, and has now declined a friend request.
A friendship is a two-way thing with both persons seeking out each other and being pleased to be in contact. It looks to me like this is not the case here now, even if it used to be. Not even a question of normal imbalance, with one contacting more than the other. You have attempted contact umpteen times , with no attempts from him, and have firstly been ignored and now rejected.
I'm sorry to say this but it sounds like the friendship is over and there is nothing to be done. If at some time in the future he were to contact you that might be different but until then, if it was me, I'd develop other social interests instead.
One of the misleading things that can happen if one reveals a great deal about oneself to another is that one can come to believe the relationship is deeper than it is. This makes it all the harder to adapt when the friendship finishes.
I'm sorry I don't have better news.
l think you've contacted him way way too much , l went through very similar with my best friend and if l was you l'd just stay away from him for a few mths, just leave him be ,nothing.
And my guess is when his gotten through his stuff he'll probably let you know,l don;t think the friendship will be lost , hopefully he just needs he's space right now.
This mate of mine, he's in the states right now so we'd email most days , mostly about women haha, but all sorts of other crapola too.
suddenly he said similar and disappeared , nothing. Sent him a couple of g'days and l hope everythings alright , nothin. So l left him too it.
3mths later l get a call from him apologizing but he just had a lot on and needed some space to sort through some personal things, He's been good as gold since.
I guess as the person on the spot you have a better feel for the situation. Maybe it depends how one-sided things were before he broke off.
Voice is a good way to try, and also being light. As Randomx says people do break away for a while.
I do hope that is the case here