It does matter to you--and he is curious as a cat. He doesn't want to wait till you are ready to disclose the info. Several things I've learned in my time (only lately-took a looong time) 1. use my caller id. 2. "No" is a complete sentence 3. If someone continues to harangue me--I walk away whilst they are in mid sentence--they can talk to themselves- they were anyway- they didn't give me room for input--so I smile and say "bye" whilst they are still talking to themselves and walk away...I do this over the phone and on skype too-"Have a lovely day" end call.

Just tell him you are not ready to impart any further information. ta da--

Sounds like he may really care for you---if he does, he will respect your wishes--tell him so.
A true friendship is based on trust, and respect for one another.

When you sound down, he wants you to tell him about it--as once you did--and you got positive results--no judgements, and he cared, you said...so when you are up to it again, you know you have someone you can talk to. That's great!

However, you do not care to talk about it now. Tell him this Period

If that's a problem for him; then tell him you'll have to pick up your relationship at another time; besides, what is it with him doesn't he like you as you are now? Why must he know all the intimate details of your past???
Is he writing a book?
Or does he just want to get to know who you are right this minute?
How about just talking right now, in this moment--or how about you start prying into his past-"turnabout is fairplay!

Then there's the funnier way to tell him, act like "Ya Know what--I forgot!--I really forgot---I slept upside down on the bed last night and all my memories are gone from that time in my life"--but say it with a totally flat face, like it's really true---

Get into the Humorous aspect of Life---it makes it all easier!!!

Like a Brooklyn girl would do (((((EVENING))))) theo