There's been a few freds about this recently which has made me feel better, as I often feel this way. Realistically I have 10 friends.
2 live in faraway county, have full time jobs and a newborn
2 live in a nearby city, but still an hour away, 2 young children, full time jobs
3 live abroad, 2 different countries, 1 recently married and I wasn't invited so guess not as much of a friend as I thought 
1 is a single mum who struggles to have any free time to meet, as the slim time she has alone she needs 'me time'
The last 2 are a couple who are quite introverted, and can be quite selfish and difficult, if you fit in with their needs you're welcome to join but don't expect an effort.
So I don't really feel like I have friends because I have no-one that I can see regularly. I have had other friendships that have fallen by the wayside for various reasons (several liars) and I think friendships from work or activities always end if you leave that job/activity or so I've found, those friendships to be quite transient. Reading several threads like this on MN has made me feel less alone, as I thought something was "wrong" with me.
I have a sibling who is Miss Popular, but as time has gone on I've noticed that none of her friendships have much depth, and her friends don't "know" her. My other siblings friendships are much more transient than mine are and always have been. I think she has intimacy issues.
I think once you are out of uni/school - making new friends is a ruddy nightmare as there is a stigma about it for women if you aren't already part of a group. I had a hard time at school and my adult friends are uni ones but we have spread out all over the place, so I don't really have a fancy a cuppa ? friend.
I have been friend dumped in the past which is painful, but now I'm on the opposite end where I need to dump a friend whose behaviour is unhealthy for me and often feels like my enemy. Ending a friendship is tougher than finding one as I feel so guilty - she's an ex colleague, but is super intense, rants and raves and is homophobic and racist. I can't carry on.