it's simple actually saya cinta awak = 사랑해 aku cinta pada mu = 당신은 사랑해(요) 그런데 부부사이에 'cinta'은 자주 안써요.. sayang을 사용하면 더 자연스로워요

Hi, Anyway the correct sentence is "aku cinta kepadamu"... but normally people will use "aku cinta padamu" to make it shorter (but if you really concern about the "tatabahasa" then this sentence is incorrect) Kepada is actually is a "kata sendi" in Bahasa Melayu which is you will use it for a person or nouns only. Example: -Surat it ditujukan kepada kekasihnya yang tercinta ~Emak memberi seutas rantai kepada kakak. but for "Pada" it will be used with the nouns to show the location/place and time. Example: -Keretapi itu akan bertolak pada jam/pukul 2.00 petang (time) -Tali itu diikatkan pada tiang bendera (location/place)