You must be very determined not to have a real relationship, what with pouring so much of your energies into this complete non-relationship.
"He says the reason we haven't met yet in person is because of his anxiety, and his general mental health after witnessing several traumatic experiences."
I can understand supporting a partner with anxiety/MH issues - but this is a man you've never met! He's not a partner. He's not even a friend. Why are you spending so much emotion on him? Can you answer that question to yourself if you don't want to post the answer here?
Bottom line, he's either lying to you, or telling you the truth. Let's look at the possibility that he's telling the truth first.
If he's telling the truth he is crippled with his anxieties, and is not emotionally available for a relationship. He needs some serious therapy, not someone hanging on to him in a non-relationship. And you need to ask yourself why you're so keep to use his anxiety to block you from engaging with other men who would be emotionally available. You are putting your life on hild for a man you've never met.
Then, there's the possibility that he's lying.
If he's lying and spinning this story of crippling anxiety, he's a weirdo who gets off on manipulating women. He likes to watch them twist themselves into pretzels trying to be supportive, to be 'nice'.
Truthful or lying, there is no possibility of a relationship here.
"Last week a person who I thought was a friend posted a picture I had showed her on Facebook (without his consent) onto a group called "Are we dating the same guy?" and its made things worse for us."
She is your friend. Are you familiar with the phrase 'can't see the woods for the trees'? It's about seeing the overall picture rather than just a few of the details. In your case, all your attention is on his trauma, his anxiety, him. Your friend is at arm's length and can see your behaviour, his behaviour, the effect his behaviour is having on you. And without an attachment to him she is capable of questioning what the hell is going on. And acting on those questions.
"He said it was because his love for me stopped him, and I'm the only woman he wants."
Really? He loves you so much he can't even work out a route on a map that wouldn't take him through that "certain place" that's so traumatic? It might need one hell of a long diversion, but do you really think it's not possible?
"We were really strong and now he is doubting himself again."
Oh, come on! You've never met!
Why are you arranging your life to make sure that you cannot be in an actual real relationship?