Thank you for expressing your thoughts and emotions on this platform. It seems like you are in a conflicting situation where you are in love with your cousin but not completely giving into that relationship because of your parents' disapproval. From the way you put down your thoughts, it is evident that your cousin has a strong presence in your life for more than a decade. Also, you mentioned she is everything to you but because of family pressure, there has been a strain in your relationship with her.
Considering the above factors, you want to be with your cousin but are worried that you might regret your decision if you go against your parents. Your concern is understandable and only way to resolve your conflict is to question yourself with "How does my life look in 5,10 and 15 years from now, if I am with the girl I love or if I listen to my parents? This will help you in getting some clarity about your future with her.
Also, if you can identify the reasons behind having doubts about your future with her will enable you to address those, and in turn, can be more confident with your choices.
If you want to discuss further on this, we are all here to hear you out.
Nandana Priya Kamasani