It does have a sexual side effect.
http://www.medhelp.org/drugs/citalopram/show/4833
Click on the Side Effects
It says "decreased sex drive, impotence, or difficulty having an orgasm"
Not sure if it affects the semen volume.
I'm taking it right now. I used to take lexapro but switched to this one. Since then, it's been easier to climax and, if anything, the semen count has increased, but don't quote me on that.
Hope this helps.