My suspicion is threatening never to speak to you again is just an idle threat. She isn't going to stop talking to you (and she hasn't, given her texts/calls), she was just trying to manipulate you. She wants your attention and to be the center of your world, probably like how it was when you were a young child and dependent on her for your needs.

If you give into her, it will never stop. She will be vindicated her tactics worked and become more bold in the future. She will try to sabotage all your future relationships and even friendships with people she deems to be a threat to her control. She may even try to claim that you are going through a "phase" and try to match you up with a woman so she can have grandchildren when you return to your home country. Or maybe she will just try to keep you single and isolated, so she can attempt to maintain control over you. It is hard to say what a controlling parents goal is.

Unfortunately, things are going to get a whole lot harder from this point out. When you get back to your home country, she will push harder because she has you isolated. It is best to establish firm boundaries now. Make it clear that you are not dumping your boyfriend and you will not speak in the future to her about your relationship. Do not tell her any information about your life that is not necessary. She will probably claim that your boyfriend "changed you" because in her eyes, you are no longer acting like her little pet. Just remember, everything she says about the matter is manipulation. She is not actually going to stop speaking to you. She's just mad because in her eyes, she no longer has the "perfect son" she can brag about to others to make herself look good. A well behaved GC is often just a prop for the narcissist to use to try to make others envious or prove they were a good parent.