Tough situation, indeed. From my point of view it is possible to make two relationships work, to give them similar importance and standing in your life. I believe that I managed to do so.
But your situation is (like everyone else's) unique and not really comparable to mine in regard some points. The biggest thing you need to realize and you need to understand is that you are making a huge choice there. Your boyfriend will never be able to reach this point officially. You are making an official vow, an official commitment there, and this kind of commitment is unique in our culture. You are choosing her over him there. You can't sugar-coat that. It will hurt him.
Having said this much, you can only follow your heart there. It is a serious decision and if you feel like this is the right action to take, if you feel her to be this important for you and to be more fitting to be this person for and in your life, then go with it. You can't postpone your life because someone else might want it to be otherwise and of a different kind than you yourself wish for it to be. Your life can only be perfect for you, you can't live a perfect life someone else is envisioning you to live (without being sad and unsatisfied, at least that's what I believe). And on an additional note: Things aren't perfect
Try to do everything the best you can and be satisfied with the result is all we can do.
Don't let your boyfriend live with some illusion of what he thinks your relationship to be. You are right to not stress him additionally (I just had a similar situation with my family, I decided to wait as well, but that wasn't something affecting them directly.) But I would advice you to sort this out as soon as possible. You will gain nothing by waiting too long. If this family business is postponing your talk endlessly, just find a decent moment to tell him nevertheless the complications in his family life.
The only thing you can do is being real. Don't hide yourself from your partner. If he decides that he can't take who you are and how you have changed or whom you evolved into, it's his choice to make. As you can only decide if you are happy with your partners, grant them the same right and offer them the whole truth about yourself.
Wishing you luck and some peace of mind.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.