Is it OK to break up with a girlfriend due to serious illness?

That sounds like an excuse you are going to make up and lie about it to make it easier to break up with her. No a girl that truly loves you will not a find your illness as a burden. An illness is an obstacle for someone just like (arguing or disagreeing is) that makes a relationship stronger. If your girlfriend finds that a burden she truly doesn't love you.

See here is the thing. When you see couples like you, sick man / woman + healthy man / woman, its not like the sick partner is holding them at gun point TAKE CARE OF ME!!!. the other partner just makes the choice because love and stuff. Here is what i think is right to do. Tell her about your illnes, and then tell her that if she doesnt want to take on the burdens of such a relationship, you are setting her free so she doesnt have to feel bad. If she loves you and choses to stay with you considering the consequences, dont feel bad about it, its her choice, and she chose it herself. Lets say you do what that guy up there told you and break up with her saying its for another girl, she will hate you, and then if you die to the illnes or something, and she finds out, she will be devastated. Im telling you, dont keep this from her, Give her the option to chose her own path. Becuase if she loves you enough to stay in the relationship considering the sickness (which is a lot of love) and you tell her "sry i got another girl fk off now k?" it will crush her soul much more then being in a relationship with a sick guy

Maybe it's a better idea to talk about the situation with her in person before you break things off.

Totally understandable and brave. However, if you tell her that you break up cause you're sick, she'll want to help. Women love to feel useful. Just tell her you break up for another girl, she'll hate you for it but will at least find another boyfriend. Good luck to you.

I would do the same thing, I wouldn't want to be a burden and I'd feel like they're only with me because they feel bad for me and I don't like that

Sure do whatever you want

Make the offer. Let her make the choice.