"People always think that the most painful thing in life is losing the one you value. The truth is, the most painful thing is losing yourself in the process of valuing someone too much and forgetting that you are special too."
Never forget who you are. What are your life goals, your passions, your purpose? If you can't really answer, it might be a red flag that you're living for someone else and not prioritizing yourself. I don't mean to prioritize yourself in a selfish way. There's a way to put yourself first and take care of yourself and also be a good partner or friend. I just mean to do the things you enjoy, set some time aside to focus on your needs or desires. What do you want, what are your dreams? We've all probably been there at least once in our lives where we focus so much on the other person that we lose sight of who we are or what we want in life.
When we take care of ourselves and focus on what brings fulfillment in our life, we treat others better, we're more present in doing the things that they want to do as well when we spend time with them, and that's more attractive to the people we are in relationships with. It's a give and take... if you feel like you are constantly sacrificing what you enjoy for the other person without them budging to share in things you enjoy or your wants and needs then there's a problem. Set aside some time each day to do something you want; even if it's just 5 minutes. Or do a weekly journal where you can just free write all your thoughts, your feelings, your opinions, what you want and your dreams. This helps you to get back in touch with yourself and who you are.
Remember YOU are special and need to take care of your needs and wants. If someone doesn't respect that and doesn't understand, or makes you feel like you have to sacrifice yourself and the things you enjoy for them, then they aren't meant to be a part of your life.