(\s|$) Match either a whitespace character or the end of the input string.
Imports System.Text.RegularExpressions
Module Example
Public Sub Main()
Dim pattern As String = "\b\w+(e)*s(\s|$)"
Dim input As String = "matches stores stops leave leaves"
For Each match As Match In Regex.Matches(input, pattern)
Console.WriteLine(match.Value)
Next
End Sub
End Module