I m running scared and am totally insecure

I am running scared and am totally insecure about my developing relationship with Dave.  Smokey left me thru his death.  I don't want anyone else to leave me.  It was not nice the first time round.  Dave makes me happy but at the back of my mind what if he leaves me.  He is a gorgeous, sexy, handsome 47 year old male.  He could have his choice of any woman on the planet.  Why me?  Why does he want me?  I am a 54 widowed unemployed 5'2" tall woman.  Again, why does Dave want to be with me?  I cannot fathom it.  It just doesn't make sense to me.   It scares the living daylights out of me.  It has only been ten months since Smokey died.  Dave and I meeting came right out of left field and is a total surprise to both of us.  This past week I have become a total insecure jerk with Dave.  I don't think I have many chances anymore.  I keep trying to push him away but he draws me right back in and I don't know why.  A lot of guys would have given me the boot by now but not Dave.  I know his patience is wearing thin and he told me I don't have that many chances left.  Why am I trying to screw things up when things are going so well with me?  I don't get it.  I don't understand myself.  It is like I am doing self-sabotage on my life. 
Confused Diane Baillie