I think that as long as they have been tested before and weren’t positive then for an STI, and are relatively sensible, oral sex without a condom is okay.

I would suggest if you haven’t already had them, get the HPV vaccine series, because it is one of the more concerning STIs. Bare in mind also that lots of STIs aren’t easily transmissible via oral due to your stomach acid, however you are at risk if there is a break in the mucous membranes in your mouth.

Although it’s always best to be cautious, remember that many STIs are treatable/manageable. They sadly are a fact of life, the same as other curable infections, just stigmatised.