Realize that there's a difference between bitterness and anger. As Maya Angelou so eloquently put it, "Bitterness is like cancer. It eats upon the host. It doesn't do anything to the object of its displeasure." Contrast this with anger -- it's okay to be angry, as long as you channel that energy productively.
Rather than trying to figure out all the different components of how to make love last, focus instead on creating an atmosphere of respect with your partner. The more you can do this, the more other vital elements of the relationship, like trust, intimacy, passion, love, and so on, will naturally flourish.
For all of you singles out there, it took me way longer than I hope it takes you to learn what it means to really know yourself. Because if someone really loves you? They won't care if you own a sweatshirt with the logo of their crappy football team on it. And if you really, truly love someone? You'll never even consider buying one.