No matter how hard you try to make people happy, some of them will simply take you for granted. Many of these individuals will be oblivious to or fail to appreciate all you do for them. It's these kinds of people you should not keep in your life.
You don't want to associate yourself with people who only care you exist when they need something -- when it's convenient for them. They may consider themselves your friends, but they're anything but. True friends are not users, nor are they opportunists.
Real friends are there for you through the thick and thin. They understand that the cornerstone of a strong friendship is giving with one hand and taking with the other. There is absolutely no place for selfishness, envy, or jealousy in a friendship or relationship. These all serve to undermine the trust and goodwill cultivated between two people.
More importantly, never seek the company of people who demand that you change something about yourself. Who are they to dictate how you should think or behave? True friends will appreciate you for who you are and gravitate toward the "authentic" you. The right friend or partner will see you as enhancing their life. They don't want you to change because they're happy with what you bring to the table here and now.
And just because you've known someone for a long time doesn't mean you should feel compelled to save a sinking ship. If the friendship or relationship isn't working out anymore, free yourself of that individual so that you can move on and meet new people who can positively impact your life. There's a season for every relationship -- one that season has passed, it's okay to let go.
The right people in your life are those that will support you every step of the way. They don't always tell you what you want to hear; instead, they provide constructive feedback and share what they think is ultimately the best course of action for you to take in a given situation. The right individuals pick you up rather than drag you down.
While friends and partners don't complete us -- only we can do that -- they enhance our lives in a big way. If you don't feel you can trust someone, don't let your guard down. Let people earn your trust. The best things in life are worth waiting for.