This is a very confusing question. My first thought was why are you asking this question. Seems obvious that you're both sick with a stomach bug. Why do you think you're not sick?
My second thought was that this isn't a real question. My third thought is about your belief that you're not nervous.
I question the statement that you're not nervous. The fact that you asked this question indicates nervousness or anxiety. You are concerned that something is happening to you. That is anxiety (nervousness) And you may be nervous or anxious about other things. Most of us are unaware when we're nervous some of the time. Many of us are never able to identify what we're feeling as nervousness/anxiety.
My fourth thought is that you're suspecting that you're pregnant and not wanting to consider that possibility. (I came to this conclusion without knowing of your other posts which indicates to me that you're very normal to be feeling this way. Others, without your history of concern, have felt this way. ) Now, I've read your previous posts and am nearly certain this is the cause of your nausea and even that of your boyfriend. You've asked about pregnancy 2 previous times now and then this.
You are either pregnant or you're not and are anxious that you might be or might not be. Do you want to be pregnant? If so, you're anxious that you're not and this is causing nausea. Or you are pregnant and are having "morning" sickness which can happen anytime during the day. And your boyfriend is having sympathy nausea.
If you're not pregnant and don't want to be pregnant you could still be nauseous because of your anxiety. Or you could have something else going on.
If the reason you don't want to take the pregnancy test is cost, you can get reliable tests for $1 at The Dollar Tree or any other dollar store.
If you don't want to take the test because you don't want to know if you are pregnant then I am further convinced that your nausea is caused by anxiety. Just take the test and know so you can deal with the rest.
I suggest that you make an appointment with your doctor to discuss this. If you can't afford to go, make an appointment with a low income clinic or the county health clinic. You need to get past this anxiety.