We have been together for 2 years but known each other for longer. He has an 8 year old child with an ex who hates me with a passion and will not allow the child anywhere near me. My partner respects this as he knows she can made access difficult and feed the child's head with all kinds if he doesn't. However, despite the fact that we love each other and want to get married and live together we are unable to do so because of this. His daughter sleeps at his twice a week and spends time there on a weekend. So there is no options for us. As things stand, we will have to wait for another 5/6 years or maybe longer for this and I really don't know how to cope with it. I want more but I know he can't give me that.

Do you know if a court order is in place regarding visitation? If not, he might want to consider looking into it. The child's mother would then be bound by the court order or face consequences of going against it to restrict access.

It would be a very unfortunate situation if the child's mother were to spew untruths to the child, but of course it happens all to often in similar situations. Since the child is 8 years old, the father should be able to help the child to understand the situation. Definitely avoiding making the situation worse with any of his own negative comments about her mother.
If you become married she won't have any choice but to have you also be around the child.

Otherwise you have a couple of options: 1) continue as you are until the child is older or the mother comes around in her thinking... 2) cut your losses now, end the relationship so that you don't have to get caught up in it, and find someone without the extra drama