I guess you have tried all the possible combinations to add line breaks in jQuery tooltips but failed. Here is my approach to resolve the problem in version 1.10.3 of jQuery UI.
In HTML part, to add "\n" to represent the line breaks like this:
<a href='#' title='The first line.\nThe second line.\nThe third line.'>The links</a>
In CSS part, you must suppress the original attribute white-space of class ui-tooltip in your local CSS file like this:
I hope it helpful.