I've developed some similar issues myself, although all but my current GF was previous to me being out as trans (I initially came out to my current GF). However all my past relationships have caused me to have lots of trust issues and worries that the other person will want to leave me, like what you were describing. All of my previous girlfriends ended up cheating on me at some point, or just leaving me for someone else and dropping me like a live grenade. i.e. chucking me out of their life, full force.
All I can say is that if you get paranoid thoughts about him, try to just not think them. From what you've described, it seems like you have nothing to worry about. If he were really trying to detach from you, I doubt he'd have emailed you 5 times today. Plus he did respond nicely to what you said to him. I've learned it's best to ride it out and let them, over time, prove that they are genuinely interested in you and wanting to stick around. If he wants to leave you, he'll leave you, and there isn't much to be done about it, really.
When you start thinking bad thoughts, focus on all the good things. Like how responsive he's been - and the fact he's still responsive.
I really sympathize with previous bad relationships messing you up in future ones. I never have and never would do the things that have been done to me, but they've made it so I have a hard time trusting anyone. Get burned enough and you have a hard time playing with fire again.