So, here’s a technique for having uncomfortable discussions where you want info that might be hard to ask outright:
If you can’t get information, give information.
In other words, lead off with sharing your status, or info about yourself. That opens the conversation to the topic you want, without being accusatory or prying. The other person then usually feels comfortable sharing their own position.
In this case, it might be something like: “So, I have a doctor’s appointment at Planned Parenthood later this week and I have to get blood work done. I’m going to get tested for STDs too, it’s been a while since I did that.” Then you might just be quiet and wait to see what he says. If he doesn’t volunteer when he was last tested, then he’s either very awkward, or not a great guy.
You could follow on later in the convo, or in a few days: “Would you like to come with me to PP? We could both get tested at the same time.”