I need to combine the functionality of single selection and multiple select into a single control. Specifically, I have a number of options. The first one is mutually exclusive to the others. So, if I select the first one, it needs to uncheck all the others. If one of the others is selected, it must uncheck the first one (if selected). The other options should have no effect on each other.

<select id="myGroup" data-native-menu="false" multiple="multiple" >
    <option value=""  >Select Group(s)</option>
    <option value="-1" selected="selected" >I am alone</option>
    <option value="1"  >I am not alone 1</option>
    <option value="2"  >I am not alone 2</option>
    <option value="3"  >I am not alone 3</option>
</select>

I installed an onchange() handler. So, I know when selections are made. But I can't seem to tell which option just got selected. So, in the example above, if the user select option 3, $(this).val() becomes -1,3. How can I tell that is was "3" that just got selected?

The only thing that I've come up with so far is to keep an array of selected options and then diff the arrays when a new option is selected.

$('select[id=myGroup]').change(function() {
    // At this point, I know the sum total of what's been selectec.
    // But I don't know which one just got added to the list.
    // I want logic that says:
    //  if -1 just got added, then unselect all the others
    //  if something else was just added, make sure that -1 is not selected
    var selected = $(this).val();
    alert(JSON.stringify(selected));
});

Is there a better way?