He's an orphan, he's ashamed of not having a family and is living alone. Has he claimed to have 12 brothers? His place isn't a mess but full of books, he doesn't want you thinking less of him. His favourite past time is solving problems set by professors that would normally challenge a very able grad sudent.
perhaps he thinks that dead body behind the sofa may be a bit off-putting?
Just pick up the conversation once more, if he keeps the story up he maybe just feels really uncomfortable there, at the end of the day it's your decision, without proof of any other relationship then you can't exactly end it based on that but if you think he's lying you'll end up not trusting him anyway. Put up with it if it's worth it, he might be having a think about things anyway, just talk to him again soon and see what he has to say.
Thats quite strange he hasn't spoke to you since you confronted him. Is he an easy person to upset?
Is his name Tony? If it is, he's probably got the foot of a person he's killed in his sink.
2 yrs and personal privacy? wut the heck , there definitly someone else in the equation, setting a gf off and actin dat way hmm...