The one thing I learnt that from when I was young is that if your friends don't call you to increase your worship then they are your enemies. Really, Some Muslims do not understand the hijab.
True friends would accept you as you are and not want to change you. This means they are worse than satan because if you say Adhubillah min Shaytan nirajim he does away but bad friends don't!
To reject the hijab is an act of disbelief. If they were your real friends they would be happy that you practise Islam and encourage you.
I think they feel guilty and want you to be like them, so they don't feel guilty, unless they are non Muslims then you should leave them.
A woman who wears an hijab is free from sin unlike a woman who does not wear an hijab who shares the sin of the man who looks at her.
The act of hijab is one of the most amazing acts of worship that a woman can do and it is contious worship.