I'm so sorry to hear that, nobody likes to find out somebody they feel they know well is capable of acting so badly.
To be blunt, what I would do is end the relationship. In my (limited) experience, when somebody starts acting like an ass when they were a nice person before, its due to guilt, or projection (wants stuff, too cowardly to bring it up, blames you cause its easier than self examination and being proactive) neither of those situations clears up without a lot of work on that persons part, and I'd rather step away and let them get their head straight instead of suffering and trying to fix or help them if they have not expressed a desire for help...
One last thing I'll say, I'm not sure if you had an actual AGREEment to use barriers for oral sex - so I'm not sure if he broke a safe sex agreement or if its the fact there was an STI involved that is the main problem. If you didn't and he's just being really defensive cause he feels guilty, I'd just sit down rationally as possible and hash out barrier agreements, if you have an interest in maintaining the relationship. The shitty behavior for a month stretch...well you called him verbally abusive, of course your friends think he's abusive too, and it makes me assume he's being abusive! Unless that's what you want to attract more of, I'd firm up my boundaries and decide I deserved better, cause you do.
And I dunno...sit down and write the top 5 ways that this relationship enhances your life. If you get stuck at 2 or 3, that seems like a good gauge for what to do about it.
If you do want to end the relationship and do it kindly but firmly, perhaps you will come out of this with your friendship intact, and can revisit a romantic relationship sometime in the future if its still what you want.
Happiness will never come to those who fail to appreciate what they already have.