Well...
sayonara = good bye
ja ne, or just "ja" = see you later (a less formal goodbye, probably more suitable for a boyfriend)
So that's out of the way. Now, boyfriend... "kareshi" or "kare" (pronounced "KAH - reh") is boyfriend, and "sukidoushi" works for boyfriend OR girlfriend, as well as general "soul mate". In other words,
"Ja ne, kareshi." = See you later, boyfriend.
"Ja, kare." = See you later, boyfriend.
"Sayonara, sukidoushi." = Goodbye, soul mate.
Any combination could work. However, I assume most girlfriends would simply refer to their boyfriend by their name and a familiar honorific, such as "-kun".
(Note: I'm not certain on this, but "kareshi-kun" or "kare-kun" might be a fine way to say boyfriend as well, while being more familiar. But don't quote me on that.)
許婚 /ii na zu ke/ and 婚約者 /kon 'ya ku sha/ both are used as 'fiance' in Japanese, however the first means more like 'betrothed, promised to marry', the second is more precise an equivalent.
Kare WA watashi no kareshidesu
'kanojou' would be the exact, but when stating something like 'girlfriend-boyfriend', it would be simply 'kano-kare'. I hope I helped = )
we say Nakagawa if we want to say inside in Japanese.
To say tennis in Japanese.........テニス
メロン is how you say melon in Japanese.
Kare WA watashi no kareshidesu
Watashi no kareshi/koibito (boyfriend/sweetheart) ha Jon desu.
'Watashi WA kanojo no kareshi desu'.
Watashi WA kare o aishite
i have no stink'n idea!XD sorry.
If she has a boyfriend, leave her alone.
Kereshi means boyfriend.. or only boyfriend.
penisfied
'Anata WA anata no kareshi wo aishteimasu'. 'Kareshi' means 'boyfriend', if you want to say 'man' specifically you can replace it with 'otoko'.
'Koibito' when referring to a boyfriend/girlfriend, 'anata no ai' when referring literally to someone else's "emotion/feeling" of love.
君 (kun)
To find a Japanese boyfriend a person can ask friends if they know of any single Japanese men. Other alternatives include online dating sites or go visit Japan.