Just because you get along well at first does not mean that you will get along for many years to come
Just because x, does not mean that~
xでも、〜とは限りません
と言うパターンがよく使われていますね。
Just because you get along well at first,
最初は仲がよくても
does not mean that you will get along for many years to come
この先何年も続くとは限りません
for many years to comeの代わりにforeverもよく使われている表現です。例えば、does not mean that you will get along forever
ご参考になれば幸いです。
アメリカ合衆国 
