I can really relate to this. I have only cried in front of another person maybe a handful of times, and never in therapy. I actually tear up sometimes, and when my last therapist told me she was leaving the field, tears spilled out of my eyes, but I had no connection to the emotion really, and it was just water pouring down my face, nothing else (couldn't control it and it frustrated the hell out of me at the time).
there's a song that I think describes my inability to feel much emotion in therapy (or around people n general)... It's called Sudying Stones by Ani DiFranco.

"Studying Stones" by Ani DiFranco
I am out here studying stones/Trying to learn to be less alive/Using all of my will/To keep very still/Still even on the inside/I've cut all of the pertinent wires/So my eyes can't make that connection/I am holding my breath/I am feigning my death/When I'm looking in your direction//'Course numb is an old hat/Old as my oldest memories/See that one's my mother/And that one's my father/And that one in the hat, that's me/It's a skill I'd hoped to abandon/When I got out on the open road/But any more pent-up emotion/And I think I'm gonna explode//There's never been an endeavor so strange/As trying to slow the blood in my veins/To keep my face blank/As a stone that just sank/Until not a ripple remains/I am high above the tree line/Sitting cross-legged on the ground/When all of the forbidden fruit has fallen and rotted/That's when I'm gonna come down//'Course numb is an old hat/Old as my oldest memories/See that one's my mother/And that one's my father/And that one in the hat, that's me/It's a skill I'd hoped to abandon/When I got out on the open road/But any more pent-up emotion/And I think I'm gonna explode

I dunno. I relate to it a lot...