What is a friend?

Today in a feeling very sorry for myself moment I wondered whether I have any real friends? My boyfriend is without doubt my best friend and I feel very lucky to have him but I do miss having a close circle of friends. I have met people since moving to a new town that I think I can call friends, when do they stop being just someone you know . someone you see regularly and become a mate ? Its different as an adult isn't it ? As kids we would just call people, hang out , knock on there door  'Is so an so coming out to play please?' As a woman in her 30s I feel a bit awkward about asking someone if they would like to hang out with me. People are busy they already have a lot going on they wont have time for me!
However I came home and did some yoga ( is it weird that maybe my yoga mat is my second best friend, it is ALWAYS here for me after all ) and I feel better. I do have mates and I don't have time for much more socialising than I already do ! And on that note I am going to send a message asking if a fellow school run mum fancies a coffee this afternoon. What have I got to lose ?