Girlfriends sometimes reply to text messages slowly, sometimes they say they are too busy or even don't reply, but they can still talk on the phone. Does he care about me? Or what?

On the one hand, you can find out whether your girlfriend is really busy through the introduction and friends, or directly ask her if there is anything you can help. On the other hand, I think you can relax. She can talk to you on the phone, which means that she is not avoiding calling you, so you'd better not have the idea that she doesn't care about you in the future, because this idea is very negative and bad for your feelings. As long as there are doubts in the relationship, try to find them, whether face to face or sideways, and eliminate your own doubts. If you always ask yourself for a long time whether she cares about me, such feelings are very fragile.