“过从甚密”可以翻译为“have very close or frequent contacts (with each other)” ，或者更简洁地表达为“be on very intimate terms (with someone)” 。
例句：
They have been having very close contacts recently, which has raised some eyebrows.（他们最近过从甚密，引起了一些人的注意。 ）
It's said that those two are on very intimate terms.（据说那两人过从甚密。 ）