First, you need to change your thinking and appreciate the power of the words that you’re using. To call yourself “illegitimate” is detrimental to your emotional well-being. That label has long been withdrawn from use for good reason. No child should ever be referred to as illegitimate and no person should ever think of themself that way. If they did, they would feel less than and remain stuck in a victim mindset.
Think carefully about the words you used to describe yourself: “having no core,” “no sense of self,” and “not feeling whole.” Not only are they hyperbolic, they are keeping you from finding solutions to your problems. If you were to imagine yourself being whole, what would you be doing and what specific steps would you need to achieve it? Would you need to go back to college and get a degree? Would you need to join classes and clubs to meet a romantic partner or make new friends? Would you need to secure a better job so you could save up to buy a home?
While therapy is a valuable tool to get people on the right track, it often fails because clients refuse to reframe their thinking. Instead, they hope therapy will provide some kind of magic to make other people different or to alter their current situation. When they’re unwilling to put in the hard work to change the way they perceive things, they will get nothing out of the therapeutic experience.
In this regard, the words of the spiritual counselor, Iyanla Vanzant, ring true. She said: “There is no greater battle in life than the battle between the parts of you that want to be healed and the parts of you that are comfortable and content remaining broken.”
If you’re unmotivated to make such changes in your thinking, you could be depressed. Talking to your doctor about this would be advisable. After dealing with that issue, you could benefit from cognitive therapy.