Plz help frnds...

plz help frnds .. my final exams are on may15 and one of my frnd always rings me up in the evening to roam around for 45 minutes and I dnt lyk at all as its become a every day routine of his go outside.. and once I go out my mind gts littl divertd .. what to say to him as I thnk if I say no he will mind it and all.. once I tld him that we should nt gk regulrly thn he tld that he knws vry well hw mch I stdy .he meant to say that he knws very well that I dont stdy so he cll me up to go out... frnds plz help what shall I do to avoid.. so that my frndshp also does nt gts ruind..plz help...