Everyone wants to feel good about themselves. Everyone wants to be confident, and feel worthy of being loved. People look to different things to achieve these feelings.
Some people look to their family for affirmation of their worth, while others look to their closest friends. Still, the majority of people feel most loved when they are in a romantic relationship. When someone chooses them to be "their person."
From what I've seen and experienced, looking to others for confirmation of your worth is very unstable. When you feel your worth is dependent on the opinions of others, what happens when their opinions change? What happens when you get in a fight with them? If they upset you, will you be able to confront them about it and deal with the conflict? Or will the fear of losing them prevent you from doing so?
When your worth is dependent on others, you cannot have healthy relationships. You cannot have honest relationships. The fear of losing their love or approval drives every decision you make.
When this is the case, it's really unfair to both of you. When you don't feel the freedom to be honest with someone, you are not truly being yourself. You're not letting them know the real you. In turn, you may not get to know the real them either.
Only when you can deal with conflict in a healthy manner can your relationship flourish. And, this is not just in romantic relationships. Like I said, this applies to friends and family as well.
When you need someone's approval to feel good about yourself, you are making them responsible for your well-being. That kind of pressure ruins relationships. You are not loving them for who they are; you are loving them for how they make you feel. When you are confident in who you are and know that you deserve to be loved, it does not cripple you so much when they fail you. Because it is inevitable that there will be conflict in every relationship.
When your thoughts of self doubt consume you, there is less time to think of others. Instead of thinking about how you can better love someone, you are wondering whether they really love you. Be confident in yourself. Be honest. Love wholeheartedly. It really is true that when you love yourself, you are able to better love others.