If astrology told you that, you wouldn't have free will. You couldn't decide for yourself whether to marry him or break up with him or maintain the status quo.
Astrology would indicate when the relationship is likely to come to a decision point--you have to decide to change the relationship in some way, whether that's break up or get engaged/married or move in together. There comes a time, sooner or later, when you can't maintain the status quo anymore. As there always does in life.
As it is, you can choose which it will be. You can decide to break up with him. You can decide to ask him to marry you. If he asks you to marry him, you can decide whether to say yes or no. It's not predetermined for you. There's a saying: the stars impel, they don't compel.
Of course, half of that choice is in his hands. If he decides to break up with you, you can't decide to continue the relationship. If you ask him to marry you and he says no, you can't change that.
