Lonely

Do others sometimes get pangs of loneliness?
I've lived alone for 20 years and it's not that I would like a partner or anything but I just feel so sad and "down" now and then.
I don't think I'm depressed as when I'm out socialising, I'm fine.
I only have one close friend now, who I go out with every couple of weeks, as the others have either moved away or died and I don't speak to her much at all in between as she's so busy with family and has a lot of other friends.
I have a lovely family who live quite close but they're busy and the Grandchildren who I used to look after a lot are now older.
I've joined a couple of classes but although people are friendly, they just float off after the class.
I miss my best friend who died about 10 years ago, we could talk on the phone for hours and I could tell her anything but I'll never find anyone like her again.
On reading this back, I sound like a right old misery but I'm not.
I don't know what advice I'm asking for really but what do others do when they get this feeling.