Well, first the aorist tense of "sevmek" is "sever." This is also accepted.
However, "to love" is a stative verb and is rarely used in the present continuous tense (unless you are McDonalds). When you translate this, it would simply be used in the simple present in English :)
Sen is always the subject. This means "the one doing something". Seni is the accusative object and sana is the dative object. Objects are "the ones that are done something to". Objects are not the active parts of the sentence.
Examples: 1) "You love me": You are the one who is loving. So "you" is the subject = Sen beni seviyorsun. 2) "I love you": You are not the active part. It is ME doing something => "Ben seni seviyorum." 3) "I am reading you a book": You are the object again because you ate not activly doing something in the sentence. => "Ben sana bir kitap okuyorum." (I am not sure of the word order here 'though. Correct me please.)