These threads end up so depressing...I have 1 sibling who is 6.5 years younger so we were never at the same stage in life, 6 and 12 or 12 and 18 are HUGE gaps. We were not close growing up and in essence we were like two only children.
I have more than 20 cousins between the two sides of the family and I was not and am not close to a single one of them. Despite 'family gatherings' etc.
In fact my mother was close with one of her sisters and that meant we spent a lot of time with her kids too, one girl older and one boy younger than me and I hated my girl cousin as she was a mean, jealous bully and I was forced to spend a lot of time with her.
I am reasonably close to my own sibling now although we live a great distance away from each other and only meet in person a handful of times a year. We're in our 40's & 50's now and it has taken years and years to get to this point.
I really don't understand people saying I'm alone dealing with elderly parents etc especially of you're married and have kids. My parents have had extreme ill health over the past couple of years and my dh has been my support - not my sibling in any practical sense.
I have a best friend who has known me since we were 12 and we're really close and she has that shared memory of our familes growing up etc
We have an only dc who is now late teens and they are sociable, popular, kind, socially really able. So much of our family experiences in general come from the dynamic of the entire composition of the family, how the parents are etc
We're very active and sociable and see our friends a lot and we have always encouraged the exact same for dd. She has a lovely circle of pals and is really happy.
The least happy of all her friends was a girl who was the 3rd child of a family of four and she was always vying for 'top dog' status in the group, causing drama to make herself the centre of attention and was very jealous of dd and another friend who is also an only child. It seemed to stem from competing for attention and having an older brother who commanded a lot of the parents focus. So, there are no guarantees really...
I think dh and I are super conscious of making dd's like as rounded as it can be and we talk about things like not taking it for granted when she comes to visit (when she goes to university next year) in the way our parents do. We have always maintained our adult lives and while we will really miss her we are prepared for her to have her independence etc
I have no regrets at all and the only thing I hope for is that she meets someone who loves and cherishes her as much as we do.