There is a slight difference. Keep in mind there is 'fond' as an adjective, and 'fond of' that is mentioned in another response. Fond can mean over-affectionate, doting. The dictionary probable shows affectionate and fond as synonyms. But 'affectionate' implies 'showing love or affection'. Consider (1) I am fond of her, but do not let her know it. (2) I am very affectionate towards her, and she knows it.