Well that's realistic, you two are bordering each other and have conflicting intrests, it bothers me more when in that situation the alliances does not start crumbling. For an example austria and france ally each other burgundy is a mutual enemy then stay buddies for the rest of the game since they will litterally rival anyone (ottoman's mamlukes, the freaking ming) before each other. I'm sorry but the emperor of the HRE having an ethernal alliance with france kind of screws up the game.
Alliances in this era were shiftning, the dutch and the english were allies against the spanish but then later fought each other a lot, just to later become friends again.