var strD = "Some text<div><br/></div>Second part of the text";

​

var strB = "Some text<b><br/></b>Second part of the text";

var strI = "Some text<i><br/></i>Second part of the text";

​

var regexp = /<br\/>(?=(?:(?:<\/b>)|(?:<\/i>)|(?:<\/div>)))/;

​

console.log(strD.split(regexp));

console.log(strB.split(regexp));

console.log(strI.split(regexp));