Getting along with each other can be really tricky. You try to express yourself in the ways that you know how, but you find that those ways are directly in conflict with your lover's. Your partner takes the well-thought-out, logical approach, while you lead from the hips, so to speak, acting and reacting on gut instinct.
It's calculation versus impulse, and you both are irritated by the other's way of thinking and communicating. Small irritations turn into bigger misunderstandings, and then that impulsive reaction mode clicks into place -- and then you, especially, forget to be tactful and kind in your rush to get at them. When we get our feelings hurt, it's natural to want to retaliate by striking back, but this is something that you aren't able to stop doing! Even if you're ordinarily a placid person, when you're together, your temper is stirred up and you end up saying things you don't mean, hurtful things you wish you'd kept to yourself. Emotional situations, especially, are grounds for faulty reasoning. You both just start reacting instead of trying to assess the situation calmly. Needless to say, this kind of chaotic energy can wear down the best of romantic connections. It's hard to feel as if your lover is also your adversary, and that's the likelihood with this aspect. Trust and respect slowly erode unless you can find a way to tone it down when you're together.