Hi Thousandmiles. I hope I can be of some help.
I'm agreeing with everything said so far. You have nothing to feel responsible for as far as his attempts go. I can understand being hurt over being lied to (which I should point out...even if you weren't truthful, I don't think it was really his place to demand such details...I'll get back to this in a moment), but his reaction speaks to something seriously wrong aside from trust issues.
Going back to the "lie," I can understand asking about partners (Not specifics...that's TMI) to an extent. It is sometimes knowledge that may want to be known. I get that. But there's two things here that really bother me. One, it bothers me that he wanted to know precisely how close you and ____ went...that's rather private information, you know? Secondly, and more importantly, it sounds like he didn't trust you to start with if he kept pressuring you over it. That is a red flag.
But as far as his attempts go, this isn't your fault...it's sad that he does this, yes, but you're his girlfriend, not his lifeline. He needs help...help that neither you nor I could begin to provide. He really needs to see a therapist to get himself straight...that is his job, not yours. And his previous girlfriends are not an excuse. To be frank, my ex before my most recent one cheated on me with my close friend and superior officer in JROTC, and my most recent...well, to save a lot of unnecessary details, she cheated, a lot (I like to joke instead of a love triangle my ex was more like a love tetrahedron). My most recent I loved like I didn't think I could love another person, I thought was the "one"...all that jazz. The frank part is this...even though she hurt me as she did, and even if I don't harbor the fuzziest of feelings towards her, I don't hate her enough to threaten to scar the rest of her life by killing myself as she watched...that is calculated and very cruel. I'm not saying he hates you as I said in my example. I only mean to illustrate what type of an action that is.
I know you love him, and I don't suspect that much of what I said is particularly what you wanted to hear. That is something I understand very well given all that happened with my ex. But you can't be his tether to a normal life...that is sweet, and noble, but it doesn't feasibly work. He will drag you down before you are able to lift him up. He needs serious, professional help.
Please know that you are in my prayers, and I hope I was of some help. I hope my post doesn't read too bluntly or too harshly. That is certainly not my intention. It's just important for you to realize what it is you're dealing with here, in my opinion. I do feel bad for him, as he obviously needs help...but you can't risk ruining yourself to try to help him.
Many hugs,
Harley