It reminds me of that conversation regarding foot-rubs at the beginning of Pulp Fiction. One character makes the point that a foot-rub has some unspoken, extremely subtle, nonspecific sexual connotations to it. The other character claims that there's nothing inherently sexual about it at all. The first character asks the second if he would ever give a guy a foot-rub...and the argument is over.
I would say it's a similar situation here, and no matter how you try to rationalize it as purely nonsexual, the fact that you wouldn't want to do this with a guy friend implies otherwise. It's not the friendship you miss...you can still be friends...but once you stopped sleeping together, you drifted apart. You (and probably her too) miss the unspoken, unacknowledged, sexual aspects of sleeping in the same bed as her.