My bad decisions

Why is it that when I want to put my foot down, say no to something, the majority of the time I do the exact opposite. Its incredible, that mistake that could sound or seem stupid is pretty damn important. Because it changes everything. All changes after that act. And timing is everything. I don't want to say that because of this the whole thing is ruined but, its pretty obvious it is. And again, I can not expect nothing from the other person, when it was me, and only me who broke my own promise. I set out to do something in a certain way and then messed it all up. The whole relationship will change, and perception of me too. And how do I stop the other person, how do I try to remedy the situation. If there is any remedy at all. Now I feel used and stupid. I could say that well, it was a fun time and that's it. A guilty pleasure. Like any other young person out there. But the whole thing is so different from what I wanted it too be. Or maybe I'm looking for it with the wrong person. But as I'm always saying communication is everything. The only way to salvage whatever is left is to let the other person know. No matter how trivial it might be for them. For me its important. And knowing what they want will help me in knowing what I should do.