Thanks for your replies!
I hadn't realised we could both go on the birth certificate - is that a new thing?
In terms of us, I am almost 30, she is a bit younger, and we have been together for almost two years but knew each other before. DSD has two very involved parents so my role is as friend and provider of hairbands and pretty things! I would never expect to have parental rights over her as it is not necessary and she doesn't need me in that way.
It has only been really recently that DP has even considered having another child - up until a couple of months ago she was very vocal about how she thought that my DSD should be 'enough' for me and that I obviously didn't love her enough therefor would treat any child we had together more favourably. It took me ages to get her to understand that living in the same house as DSD doesn't make me her parent, not does it give me any of the 'rights' or 'benefits' of being a parent. She is not my child.
But that doesn't mean that us having children would be negative for DSD. Having siblings is great!
Its all very confusing and I am not sure if I am explaining it very well. I dont want to coast along and then realise at 38/40 that my window of opportunity has passed me by. But I love my partner and I think we would be amazing parents together.
I understand the issues surrounding adoption and having biological kids as well, but I do feel that there are many more benefits than there are negatives - DSD would have a sibling, someone for ever, someone to moan about us to etc. I think that there is only so far we can go in managing the environment for our kids before life becomes impossible for other people involved. If DP wanted DSD to have the most untouched by reality life then she should have stayed with her ex - but that isn't real life! And then I wouldn't be involved with them! It swings and round abouts - does that make sense?
DP does have issues with needing to be in control all the time and I think that is where alot of this stems from. But its not that easy to point these things out - studying peoples flaws just seems cruel sometimes. And I don't want to hurt her.