I wouldn’t necessarily dump him for being non exclusive when we were… non exclusive. I don’t blame you for being put off by it, depending on how seriously couple-y the “talking phase” was going, it might have been reasonable for you to expect that he had tapered off on the other girls he was dating and sleeping with. Just the circumstances of everyone’s talking stages are different so it’s hard to say if sleeping with someone else is a dealbreaker all the time.

However, he was irresponsible and unsafe, and gave you an std! I would dump him for that.