I don’t know if I can handle a poly relationship anymore. I get so upset knowing my bf and I are fighting and he’s running off to some other person and spending the night and having a great time with them while im home crying and upset. he always leaves me to go off and be with someone else and it’s really hurtful especially when i’m upset or we’ve been fighting. i just don’t know how to cope with this

It sounds like there’s a specific issue here, rather than polyamory in general: your partner going to let off steam with another partner after bringing negativity to you. The first step is to talk to him about this. You can say something like: “When we fight, and you leave to see another partner without resolving our fight, it really bothers me. Can we agree to not run off on each other during a fight, even if we have somewhere more pleasant to be?” 

Then, you two need to work on your conflict resolution, so you can actually resolve said fights. Are you often fighting about the same thing? That issue needs to be addressed, whatever it is. You two can consider reading about communication strategies or seeing a couples counselor together to learn the skills that can help you move through conflict without having to run from it. Not every fight needs to end in a happy, sitcom-style resolution, but you should be able to reach some kind of conclusion where both of you feel okay about letting the conflict go before one of you just leaves the situation.

If he refuses to do any of this - if he insists on just running to other partners to escape any negativity in your relationship, if he won’t work with you on reducing the number of fights and having healthier conflict - then this might not be a healthy relationship. But first, give him a chance to understand where you’re coming from and address it alongside you.