I have recently begun experimenting with anal stimulation on my 19-year-old boyfriend by penetrating his anal cavity with my finger. About 2-3 inches in my finger comes into contact with something small, smooth, kind of pointy-ish, and kind of hard-ish (feels almost similar to cartilage but not quite). I don't know what this is and I don't know if it is something normal or something to be concerned about. Because I've never really had any experience with anal stimulation before, I'm not really sure what is normal and what isn't.
My boyfriend has had a history of external hemorrhoids, so could it just be an internal hemorrhoid? How should I go about telling him about this without sounding weird or embarrassing him?
Any and all help is greatly appreciated.