Uhh...

You must admit that a truce is made to serve a purpose, like defeating a common enemy. When it has served its purpose it can be discarded. For example in our game we both dominated thanks to our alliance but then at that poin all of my borders were surrounded by you whereas you had other fronts to expend into. Hence it would be not only pointless for me to keep the alliance but even harmful because I would loose my first spot, so I warned you and expended, no offense but there really is no reason to get bitter over it, its just a game...

Sorry by expended I mean expanded*

In that case, you should offer a truce, let people expose themselves to you and take advantage

Either give notice, or don;t offer a truce at all.

You are the most self serving player I have ever come across

should not offer, that should say