How can I get my boyfriend to be interested in sex again? When we first started going out over a year ago, he was amazing. Then he just lost interest.

Have you talked to him about it?

Spice it up, no doubt after a year your sex life has been very predictable and routine.
Change up positions, aggressiveness, dominance, trust me, it was what I would want.
Mind you this is only a temp fix, as there might be some deeper emotional/relationship problems then just attraction or a hot sex life. Maybe he's been depressed lately, who knows.
Try mixing it up and see what happens, if there's still no interest (give it a couple tries, you might get him on a off day) maybe there's something your missing.

Have you tried talking to him? There may be forces beyond your control effecting him, like job stress, money, what have you. He may be tired of the type/quality/quantity of the sexual relationship. The both of you can make changes to fix that. But if he never tells you what is going on, you'll never know. Also, don't be shocked or angry at anything that he wants that is different sexually. Never make him feel bad about having different feelings, unless that is, they are contradictory to law. (i.e. prostitution, children). Research anything he wants to try that is new to you before you put the kabosh on it. You might like it. Most likely though, he is so used to you that he doesn't feel the pressure to please you sexually. So let him know that you'd still like to try it every once in awhile.