What if, since im doing nofap, the next time i ll make love with my girlfriend I cum very quick due to full balls? It ll be humiliating
No, do you understand how ridiculous that sounds? I am in 126 days and have not ejaculated, I don't feel like my balls are going to explode. You're fine.
Even if it happens - so what? Tell her about it being possible. It's your girlfriend, not a hooker. There is a subtle difference between the two, contrary to the general belief nowadays.