If its that much fun, it doesn't feel like volunteering

I usually spend about 4 hours each Saturday at a nearby thrift store that supports a great charity/ministry.  The woman who runs the store is just great.  She's like the sister who got separated at birth, you know?  We have similar backgrounds with similar stories and similar problems.  We have the same sense of humor and have a really good time working together.  She is married while I am not and she has two kids to my one, but I enjoy being around her so much!
I'm actually a little nervous about transitioning our friendship out of the "work"place, for fear of wrecking things somehow.  Silly, huh?  What a treasure she is for me!