Out of hand Situation?

Im super confused, i been having this on and off relationship with this guy for about 7 yrs... the last 3 yrs hes been dating someone else, and i just been doing me! At this moment hes in a rough situation and i decided to be a friend and show him suppourt for whats he's going thru, but the relationship is getting out of hand, he wants me to be there more than a friend, but not like a relationship and since i been there before and is not what i want, i been trying to be open with him about it, but he just wont take a NO for answer! Im just not sure how to deal with thi situation anymore... bcs i care for him and i want to be there, but i still have feeling for him and i dont want to go down the same road again.