What to do when you feel you are not good enough for someone?

In my opinion, you talk about your insecurities with that person. Let that person assure you that you are wrong, and little by little, tell yourself everyday that you are worth it. Gradually, your insecurities will fade away once you believe in that. Also, if the person makes you think that you are not worth them even after confrontation, then, leave that person. Because, that would mean that they do not truly appreciate you.

I will first loose contact with who ever makes me feel like that and later get in touch with a therapist to help me build my self confidence again

It simply means that you are not aware of your own strengths. Start counting them down you will realize you are as good as any one else. Furthermore remember that may be one of your strength is extremely valuable. Like honestly is a very expensive gift don't expect from cheap people.

Think about why you believe this. Is the person worth you worrying about this? Is the thing you think they want you to change something you, personally, want to change? How important is your relationship with them? Are you happy with how good you are youself?

What is it that makes you feel you are not good enough for them? Sit and write some positive qualities of yourself that you see in yourself and that you think other people might also see. This might help when you’re feeling that you’re not good enough for someone

I make myself realize that someone better is waiting for me and I'm only good enough for him but also we're perfect for each other.

Know that no one is perfect or good enough, we all have our own flaws, we also have our own good points. You just need to be true and express your thoughts to him/her to remove that anxiety. Because for me, if that someone truly loves you, you won't have to compete, they will love every part of you, good and bad.

I look to myself and improve what I wish to improve for my own reasons and raise myself to my desired pedestal. As long as I feel fine or even better in my own skin, then I'll always be good enough for who's right for me.

Learn to find yourself and love yourself before even thinking you aren't good enough for someone, everyone is good enough for someone. Don't let that define who you are let YOU define who you are as a whole.

Tell that someone how you feel. They will tell you and help you understand that you are a great person!