It's not like everything was going great and then the second his cock touched her you crumpled up into a ball of tears because you can't actually handle threesomes. He was being inconsiderate, you were done with the sexual encounter, they'd already both been satisfied, you asked if they could stop (how did that part go, were you chill, was she chill , or was it super awkward?) which is In fact perfectly reasonable in this context, then you got pissed at him for being inconsiderate (which is reasonable) and he got pissed at you for, well, I'm still not sure what. Where is your failure here?
Also, there is *always* room for more communication and groundwork. It is normal for things to still surprise you and be hard or confusing from times to time, because even if you think you've got something worked out, there will always be a new variable. It's all in how you deal with it. Do you keep your cool and express yourself, or do you freak out and shut down? That goes for both you and him.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.