What do you think about this..?

lately i have been spending alot of time with my 20year old male friend and im a 17year old girl, he wants to hang out with me more often, even though he knows that i won't date him, my friends don't trust me to be alone with him because he's very promiscuous with girls and i just found out that he has has with a 16 year old. he isn't perverted around me unlike with other girls he seems very protective over me...what does this mean?