I want to be with you in Japanese?
会いたい /ai tai/ literally means 'Want to to see', which
figuratiely is used in the same meaning as 'I miss you'.
恋しい /koi shii/ is an adjective literally meaning 'missed,
yearned for'. In this case it's used like あなたが恋しい /a na ta ga ai
shii/ literally meaning 'You're missed/yearned for.' which
figuratively means the same as 'I miss you'.