Disclaimer: I am not a medical professional, nor have I studied medicine or mental health.
When I started on Prozac (fluoxetine), it made me feel dreadful. I'm on an SSRI for anxiety, not depression, and a possible side effect of Prozac is anxiety. I felt like my brain and my arms were constantly tingling, I depersonalized even worse than I already was, it was terrible.
Then, I switched to Zoloft (sertraline). The same class of drug, but it made a world of difference. The only side effects I felt were a little digestion discomfort for about a week. The tingles went away the very day I switched pills. My sister, brother-in-law, and dad are all on Zoloft and they speak super highly of it because they didn't experience any side effects.
I've heard that Zoloft is regarded as a gentler SSRI, but I can't verify if that's true/what makes it true. There are soooooooooooooooo many different kinds of antidepressants, even outside of the SSRI class. Chances are, your boyfriend will find one that makes him feel good. I understand he has a fear of being sick, and honestly, getting on an antidepressant can actually help to assuage that. At the worst of my anxiety, I was paranoid that I was going to have a seizure at any moment. No idea why, I don't have a history of them nor does anyone in my family, but the thought of going on an SSRI and reading the risks of serotinin syndrome (which seizures is a symptom of) terrified me. Funnily enough, about a week after starting the Zoloft, that fear completely left.