Relationships are hard and take a lot of work to build strong. If only one person has been doing this work while the other person just reaps the rewards, the person doing the work will eventually burn out. Once this happens the relationship may be doomed unless the other person takes over and works on building the relationship.
If you don't know what to do for the relationship to make it better than take some time to research all you can about relationships. There are hundreds of books and resources on the internet. Treat the other person how they want to be treated. Each time you do not treat them how they want to be treated you are just telling them that they do not matter. Your actions always speak louder than worlds.
If you are the person who has been doing all the work in the relationship and are too exhausted to keep this up - remember that you deserve better. Life is too short to be in a relationship where you are doing all the work. You need to have someone who respects you enough to support you and be there for you.
For those who are the ones who do all the work - you do have value, you are important, and you really do deserve someone in your life who will put you and your needs first once in a while. Don't settle. Set some standards of what you want and stick to it.
Finally, to those who are the ones in the relationship that is falling apart because your partner is telling you they do not feel supported - then become a true partner. Support is very important to everyone not just you. If you don't know how to demonstrate this support than ask and follow through with how they want to be treated!