As you’ve discovered: Avoiding a problem sometimes creates yet another one. You now have both the issue of who you are dating and the fact that you’ve been living a lie for so long. Your parents will rightfully see this as an indication that you aren’t as mature as you think you are. Further, they are likely to think less of your boyfriend because he participated in the lie and didn’t insist that the two of you work it out with your folks.
You have a very, very difficult decision to make. If your father represents the feelings of the whole family, making a life with your boyfriend will mean losing your family of origin – at least for a time. People don’t change just because we want them to. What you can hope for is that the family will eventually come around. They are more likely to do so if you and your sweetheart make a good life for yourselves and if it is clear that you love and cherish each other. Further, people are more likely to make up if they part ways without loud, angry words, incriminations, and accusations. If instead you simply, clearly and, above all, calmly tell your parents how much you love them, how much you appreciate all they’ve done for you, and how much you regret that your choice is something they can’t support, they are more likely to reach out to you after they’ve had more time. After all, they love you and don’t want to lose you as much as you love them. If there is someone in the family who can be an ally, do have a conversation with them to see if there are ways they can lend their support.
I don’t know enough about the situation to know about timing. I do know that the longer you live a lie, the harder it is to undo it. I suggest that you get yourself a counselor. You need an ongoing relationship with someone who can look at the situation objectively and who can help you through the difficult conversations and decisions that are coming your way. Your boyfriend should participate. If the two of you want to be together, you need to take on this big challenge — together.
I wish you well.