If there is obvious problems occurring
but your think your boyfriend has potential to be someone who is worth having a relationship with, you could try talking it over with him before coming to an actionable decision.
The next time he is oblivious to how it becomes impossible to not have their relationship bleed into the mood of yours, try stating the obvious, not all people feel threatened by something as little as a suggestion
If your boyfriend is frying eggs in a pan without butter and starts getting worked up because they are sticking to the pan, is he the type of person that will bite your head off for letting him know the butter is in the fridge?
after biting your head off does he -- the next day -- explain the reason you deserved that nip in the bud is because you are trying to control and interfere in his life and you need to deal with your insecurity issues regarding cooking breakfast because it isn't his responsibility to walk on the egg shells and if you need someone to pussyfoot around your inability to maturely handle polyamory you are so obviously mono he finds it amusing you can't see the forest through his great advice that any monkey could stumble through polyamory easier than you could
but you just don't listen do you
because if he is the type of person to decided this new girl is mature enough to decide she will try to cook eggs because he offered that as the alternative to breaking up -- and she is as good as a cook as captain obvious -- some people have a heart to show her where the butter is rather than watch and criticize or complain that there's no toast after she is a good enough sport to not bail after being set up and then knocked down
Some people are mature enough to be worth some effort to have a relationship, but if you aren't compatible or have no problem with not having an element of abuse in your relationship dynamic it may be wise consider opting out of mature and responsible style of relationships
but don't fell bad, you just were too kneejerky and emotional to handle polyamory. If you read around and search the tags you might get a sense of what it takes should you one day decide you are ready