According to rxlist, Remeron (mirtazapine) lists "thinking abnormal" as a significant side-effect, (3% in those taking active as opposed to 1% of those taking placebo.)
It also lists agitation and anxiety as frequent side effects, with delusions, hallucinations, manic reactions, neurosis, and paranoid reaction as infrequent side-effects.
Nearly every anti-depressant on the market has sexual side-effects. Remeron is one of the nicer ones, as all its side-effects are listed as infrequent, and an increased libido is actually one of the side-effects, although it can cause (again, infrequently,) impotence.
Celexa (citalopram) lists the most commonly-occurring side-effect as ejaculatory problems, most commonly ejaculatory delay.
I guess it's a question between whether that'd be a problem for you (as nearly every SSRI has those problems associated,) or whether you can handle the paranoia or whether the paranoia will diminish with further treatment as your body gets used to it.