The next step.

So I've been with my boyfriend for 7months and I've been on the pill for 3weeks and I think I really want to have sex without a condom. We've never had sex without one but I'm nervous about STI's. My boyfriend has had one other partner besides me and I think they had unprotected sex before. I don't want to just be like "I think you have an sexually transmitted disease" but I really want to say something, that that is what I'm nervous about, idk how clean his past girlfriend was. Please help with some advice or a tip or two.