I’m finding it almost impossible to give you good advice since I don’t think that you live in the US & any advice I might come up with is based on my experience with US laws!!!
I was married to an extremely abusive man whose daughter lived with us. I loved that little girl with ALL my heart; so, I accepted abuse as part of my life until it got so bad that I couldn’t take it any longer. At one point, the pain from the abuse outweighed my love for that child. My husband kept telling me that IF I left that there was NO place that I could hide & he would find me & kill me. At some point it dawned on me that death would be kinder than the life I was living & finally told him it was over & to do what he felt he had to do as I was dead inside already. Long story short, HE moved out & I got my divorce!!!
In your case with your children almost grown, I think that I would hold out for the 5 years to give your daughter time to reach adulthood. That will stop part of the manipulation of the children that he’s holding over you. He will be able to influence the children but he can’t control you with them. As adults, they will be free to choose how they feel about you!!! IF your boyfriend truly loves you, he will be willing to WAIT for you to become FREE!!! IF, by chance, he doesn’t wait,you will know that he never truly loved you & you are still FREE to live your life on your own.
Now, to the boyfriend…I’m assuming that you live in one of the countries where you can be stoned/put to death for adultery. Once again, IF the boyfriend truly loves you, he will WAIT for you to become FREE. IF he doesn’t wait, you will know that he wasn’t worth risking death for the sex!!!
Did you want a divorce before the boyfriend or is the boyfriend the ONLY reason you want the divorce??? Since I don’t know your country’s divorce laws, you’re on your own there.
Good luck no matter what you decide!!!