Django models not allowing one to many relationship - django

Question

Having a really tough time wrapping my head around creating this model set for Django. Currently I am creating a site where a user can click the article to decide that he or she likes the article. I have set up the models to include article, favorite articles, and user. However, currently the way I have it set up is for it to only allow the user to have one favorite article, not two. I am using the ForeignKey field and that is not working. Here they are
from django.db import models
# users/models.py
from django.contrib.auth.models import AbstractUser
from django.db.models.signals import post_save
from django.dispatch import receiver
import uuid
class Article(models.Model):
title = models.CharField(max_length=120, primary_key=True)
content = models.TextField()
url=models.CharField(max_length=200, null=True)
category = models.CharField(max_length=250, null =True)
def __str__(self):
return self.title
class CustomUser(AbstractUser):
username = models.CharField(max_length=50, unique=True, primary_key=True)
git = models.CharField(max_length=200, null=True)
homepage = models.CharField(max_length=250, null=True)
def __str__(self):
return str(self.username)
class FavoriteArticles(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
user = models.ForeignKey(CustomUser, on_delete=models.CASCADE, related_name='user', null=True)
fav_title = models.ForeignKey(Article, on_delete=models.CASCADE, related_name='fav_title', null=True)
reasons = models.CharField(max_length=120, null=True)
favcategory = models.ForeignKey(Article, on_delete=models.CASCADE, related_name='favcategory', max_length=250, null =True)
# def __str__(self):
# return self.user