my ex said he wanted me back, I tried and it didn't work so we stopped talking. He's been seeing someone else but he messaged again to see me. Should I tell him to fuck off because of the new girl?

I'm sorry you've experienced a breakup again. It's not an easy thing to go through. Now you're having to deal with the breakup AND seeing him with someone else. You said he's dating someone else and now messaging asking to see you again. Perhaps you can ask yourself this question - If he is with someone else and is messaging you asking to see you, do you think if he was with you that he would be messaging someone else asking to see them too? Do you feel like there are some unhealthy boundaries here?

What does your heart say to do? What does your logical mind tell you to do? I always find this super helpful... if you are ever in doubt about what decision to make, figure out all the possibilities and then choose the one that leads to the most love. In your case, choose the option that leads to the most self-love. Will you be happier with or without your ex? What is it exactly that is leading you to want to entertain the idea of reAl-engaging with him again? If he messages to see you again, think about what you want before you consider his needs. You are the most important person in your life, so I would pay attention to what you truly feel is right and the best option that leads to self-love. It’s okay for him to want you back but take some time to think about what you really want.