Sharing my unpublished thesis with other students? The other day a former classmate asked to read my thesis and I don't know why but I got a little concerned about it and just told him honestly that, "I may do future work based on my thesis submission so I don't feel comfortable sharing it with you at the moment."

Am I right to feel this way?  Is it common to keep your thesis between you and your advisor - and potential researchers who may want to work with you? Or should I really "put my thesis out there" and share it with others who want to read it and that the more people who read my thesis the better?

I somehow viewed him as a competitor, when he asked me that, but he's a close friend.  He doesn't have any thesis / supervised research experience and said he wanted to see what I did.  And now he wants to do research also and try and join a research group, etc.
Of course you should share your thesis: the purpose of doing research is to increase and spread knowledge, not to keep it secret.


  Is it common to keep your thesis between you and your advisor - and potential researchers who may want to work with you?


No, it's not, and I suggest you to ask your advisor what he thinks of such an idea.


  And now he wants to do research also and try and join a research group, etc.


Well, this is a good thing, isn't it?