What is the difference between someone interested in you & flirting?

What is the difference between someone being being friendly, someone interested in you and flirting?  I haven't been in the dating game for many years.  I just lost my husband on Sunday, November 15, 2009.  I went to Legends Bar and Grill down the street from me with a girlfriend.  This guy talks to me when he sees me there, which is not very often.  His name is Bill.  When Smokey and I would got there, Bill would come over and talk to Smokey.  I thought he was a mans man.  Now that I am single, I told Bill Smokey died a month or so ago as I don't remember.  Now when he sees me at Legends, he comes over and talks to me for a few minutes.  I think he is just being friendly to me since I lost Smokey.  On the other hand he could be flirting with me or interested.  Am I so out of it that I can't tell the difference?  I feel so stupid.  I have been thinking about this for the last five days.  It is driving me crazy and around the bend.  I probably am just making a mountain out of a mole hill.  I am the one that should be commited.  I know one thing that makes me shy no matter what you guys thinks, he is going through a horrible divorce.  It makes me think no matter if he was flirting with me or not just to lay low for awhile and not push this.  If he is just being friendly, keep it that way.  I am divorced.  During my separation, I met Smokey and we got together.  I got officially divorced after Smokey and I were together for 4 years.  I wanted the legal divorce so it was official.  Smokey never pushed me for it.  He was such a gentle man.  There are not too many gentlemen around any more.  They are dinosaurs, which is a shame because I appreciate the dinaosaurs.  I want another one in my life.  We shall see.  I haven't been back to Legends since.  I don't go alone to a bar or grill.  It is usually either my brother Don or friend Carol that want to go.  I think I have an obsessive compulsion thought process when I can't let it go and have to chew it down to the bone, the bone to ashes and then swallow it down the throat.  I wish I knew how to stop the obsessive compulsive thinking.  It drives me nuts and I don't want it.  Thanks for letting me vent all these frustrations out of my body.  I am totally frustrated at the moment.