君こそあの時、あの場所によくいてくれたねって英語でなんて言うの？

"I'm glad that you were there"＝「私は君がそこに居てくれてよかった」

"at that place and time."＝「あの場所であの時に。」

「君があの時、あの場所にいたからこそ話しかけることができて今の僕たち(の関係)があるんだよ」を訳すと↓

"Because you were there at that time and place, we were able to talk to each other, and have our current relationship."