Buddhism opposes fortune-telling, tests, and theories of time. People who do math call it evil fortune. Your boyfriend's father is not a true Buddhist.
If you are willing to be a branch in the earth, they are both trees, so they may not necessarily conflict with each other.
Bodhisattvas are afraid of causes and sentient beings are afraid of consequences. This is not the case and is a misinterpretation of Buddhism. What he means is that the law of cause and effect is not satisfactory at all, all karma must be repaid, and the sky is wide and open, and there is no omission. Bodhisattva understands the law of cause and effect and stops evil from the source and promotes good; while sentient beings do not know cause and effect and do bad things but hope to escape the punishment of cause and effect by luck.
If you and your boyfriend truly love each other, you should reason with your boyfriend and let him convince his father. Only when love is the foundation, mutual tolerance, no conflict, and conflict resolution can we have a harmonious family.