Your bonobos evolved sapience? Great. They manage STIs the same way humans do.
Step 1: They use protection
As others have pointed out, condoms are a pretty primitive invention. If your bonobos have decent intelligence, they will realize pretty quickly that STIs spread through sex and will take steps to protect themselves. In fact - you say they are a female- dominated species? Let the women insist on them. No condom, no sex.
Step 2: Good hygiene
They wash themselves before and after sex. Where? In the river, doesn’t matter. They have indoor plumbing? Excellent, the shower then. They also use soap. Oh, and wash their towels before and after use. I assume they have towels. Everyone knows civilized beings must have towels. Even Douglas Adams agrees.
A towel, [The Hitchhiker's Guide to the Galaxy] says, is about the most massively useful thing an interstellar hitchhiker can have…
Step 3: Testing
They test for STIs. Often. There are actually government-funded STI pop-up testing sites on every street. As a matter of fact, there are even bonobo-urologists and bonobo-gynecologists, and most bonobos go for regular doctors visits every month.
Step 4: Antibiotics
Horror of horrors: a bonobo gets an STI. It’s a good thing they’ve discovered antibiotics. Stole the idea from that extinct human species, actually. Doxycycline, azithromycin, penicillin… you name it, we make it. Turns out those humans were good for something, after all. Ah, the disease is not curable? It’s lucky we have medications to manage the symptoms.
Step 5: Vaccination
You want your teenage bonobo to stay in school? Don’t want to lose your job? Intend to go into politics? Make sure you and your children are STI-vaccinated. Oops, bonobo vaccines haven’t been invented yet? Well then, there’s always the smallpox method: get them exposed while their young. Preferably to the not-chronic, completely curable type of STI. This way they will be immune to those when they grow up.
On second thought, why not make all bonobos immune? They can’t get STIs because they’ve evolved to be resistant to them. How convenient.
