Inferiority complex. He wanted to be able to be an equal in their relationship in terms of finance and status…
I agree he has issues with inferiority complex but do they all need to belittle the one that they like? If he truly liked her, he wouldn't have disliked her rich family status. That will always be part of her identity and her life. He never knew her because she doesn't act like a rich spoiled brat like other similar characters in dramas do. So relieved when she let go of her feelings for him before her 2 month vacation.