Do you think I'm a bad person if I try to discourage my girlfriend from doing a PhD?
Why don't you want your girlfriend to get a PhD?
I think it will take up so much of her time, she won't have enough time for me.
You should support your partner getting an education. It's probably her dream and you should support her. She'll make plenty of time for you and your relationship.
I really don't think she'll have time for me because she'll be so busy with her studies.
Your girlfriend needs your support because graduate school will be very difficult. Getting her degree is her dream and you should love and support her so she can achieve her everything she wants.