Another point you may want to think about is that your other half may well want sex as much as you do, the problem may not be their sex drive. Perhaps they are satisfying themselves in another way. Masterbation is very common within relationships.They may not think YOU are that hot.Perhaps you are too wrapped up in yourself to be found sexy.
Try being a little more romantic with your partner. Make dinner, buy a small token of effection. Give them compliments. Take responsibily for the relationship. Look at your own faults. The most effective way to change a person is by influence This is also very hard, because it means biting your tongue for example if they say something to provoke you (remember it takes two people to argue). Often a person stops giving because they are not recieving. You may be offering to give your partner sex, but are you giving them love.