Pleae help

Question
Hi,
First I wish to thank you in advance for your help.  I've had my cat Blackie for 8 years now...he was a stray that followed me home one day.  He has been an indoor/outdoor cat, and I always make sure he has flea medication on at all time.  Lately he has been acting strange...he never wants to come inside the house anymore.  It's come to where i had to put his food bowl and water outside.  He's has always been a very affectionate cat and still is...if i go outside he follows me around but when it comes to going inside...he refuses.  I've picked him up and brought him in...but as soon as he comes in he meows and scratches the door until i put him back out.  It's almost as if he's afraid.  I don't understand what is going on and i'm very worried about him.  He always loved sleeping inside the house...now he refuses to even come in.  Do you have any idea what could be wrong with him?  

Answer
How old is Blackie now, and is he neutered?  Has anything changed inside your house?  Have you brought any other animal or person into your house recently?  Cats are extremely sensitive to change, whether it be moving their favorite chair, introducing a new pet or family member, or changing their routine in any way.  Are there any changes in his eating, urinating, or defecating habits?  When he is inside, does he seem to shy away from anything or any particular area in your house?