Im not sure what you are asking, if you are asking if we need to sacrifice everything (sometimes i bloody well feel like i do!) or whether you are being selfish for deciding to have only one child.
I am a parent of two lots of only children (huge age gap). I haven't been able to maintain any of my interests this time around as my support network consists of DP and thats pretty much it. Not moaning, just pointing out that unless you are a) really lucky to have people to baby sit etc, or b} able to organise professional childcare - pursuing your own interests is probably just as difficult with one child. Do i think having one child is selfish? Um, no - not at all. Sometimes i think, and have thought in the past - oh yes, it would be nice for DD to have a brother or sister and then i remind myself on how much friends and relations siblings bicker!! It would drive me nuts to have to be referee all the time. Seriously nuts!!! I too am an only child and i don't feel i suffered for it - i am a tad spoilt though (no, very spoilt!).
I have learnt a few lessons on the way of parenting one - and that is to make sure you establish a little group of friends for her really early on - i didnt do this with DD, because i was a young mum and the other mums snubbed me (or my imagination, i dont know). I make sure i get involved in stuff now - it drives me nuts, so that is a sacrifice i suppose.
As for your FF, you did what was best for you and your baby - no one can ask more of you than that!
As for sacrificing things, you do, don't you - i would kill for a lie in, for an afternoon sleep, for some time alone with DP. DD is nearly four and starting school in september, those things will come back.None of it really feels like a sacrifice, but if you were to list the things you didnt do or had to do as a parent then it would appear that you had basically sacrificed your entire life. Its not about that though is it - its about what you get back too - im sure you adore your DD and you are quite happy to do whatever it is that you do together (everyone enjoys different things).
I think sacrifice is a very strong word actually, because if you feel like you sacrificing things, that is one step from resentment. If im honest, i do find i get pretty close to that sometimes, but we all do.