Op, the issue is not that he isn't entitled to love someone else, and leave his wife. Of course he is. Like all of us he has a right be happy.
The issue is that you are applying pressure on him to meet his children - and in your words 'have a proper normal life'. You have said throughout your posts that you will give him 'a timeline' and 'time scale' to achieve meeting his children and being included in family events. You say over again how you want to move on to 'the next stage' and your wish for a 'normal' life together. Your aim is clear.
What you are missing is the part where the ADULT children have decided they want nothing to do with you, as is their choice. Given they are adults I am sure they are more than capable of telling their mother that they are perfectly within their rights to meet you, but they choose not to.
You are not welcome within their family unit that includes your bf.
You have commitment from him now in full view, wanting to take your year long fling to the 'next stage' but you claim on here to be happy not to be invited to events. I beg to differ.
My guess is that you are putting your boyfriend under considerable pressure to meet his children, you are putting him under considerable pressure to start stepping up and offering you the commitment that you are secretly longing for, and he is pushing back and blaming his ex wife.
His adult children don't want to see you.
His extended family do not want to see you.
I doubt they ever will. They have a very different take on events, for sure.
I would not count on any kind of proper commitment from him any time soon either, he got involved with you too quickly on the rebound from a very messy painful separation from a long marriage, and his family fell into crisis.
He is entitled to whatever he likes, but so are his children, indeed his wife. You are neck deep in a very serious family tragedy, and you are now cast as someone that has only made things worse for all of them. I can't their opinion ever changing, and it is something for you to consider when you look to the future.