Stop Being Used
One of the tell tale signs of someone who is trying to manipulate you or trying to get you on the hook is when they try to secure your insecurities. They want to know all about you, but specifically what gets to you, makes you hurt, makes you lonely, or even makes you scared. They do this because they want to gain your trust. They want you to rely on them and become dependent on them. When they have access to your life, that is when they can take advantage of your life.
If you are always doing things for someone else in any particular relationship, and they are never doing anything sweet or big for you, that's a problem. Now, don't hear me wrong. I'm not saying that you need to only be good or kind or noble when you think you are going to be rewarded in return, but if someone cares about you, they are going to return the favor. It is like how we shouldn't say "I love you" just to hear it in return. If someone loves us, which they hopefully do, then they should want to say it back. Pay attention to the one-sidedness of the relationship. If it is leaning all on your side, then that's a problem. It shouldn't always be all on you to help someone get through a tragedy. It shouldn't always be you who is paying for things. It shouldn't always be you who is going out of your way to do something nice for the other person.
Sometimes when you act like a doormat, whether you know you are doing it or not, the other person will actually become reliant on you. They may feel like you are their safety net and if you leave, or God forbid, stand up for yourself then they might feel personally attacked. They might think you are being extremely selfish to not listen to them all of the time. They might think it's unkind or uncool of you to want things in return. When you give them all of your love, attention, time and they don't give anything back then they are probably going to feel sort of entitled to it.
Any relationship that is a one way street will (and should) eventually come to a dead end. Relationships should be a two way street. If it is not it will get sour. One of you will become entitled and the other one will slowly get angry and resentful. You can't leave a sour relationship unchecked because it will eventually turn bad on you and you'll wonder when it went wrong. The answer is this: It went wrong every single time you didn't stand up for yourself. It went wrong every time you told yourself "not again" but didn't really mean it. It went wrong every time you believed for some reason that you don't deserve any better than this. Stop believing that you deserve to be treated like this. Start demanding real love, and stop settling for anything less than that.
It all starts with you.