How do I tell him I’m done with being his fallback?
You don’t need to. Just STOP BEING HIS FALLBACK GIRL.
Look, it’s not like you entered into a formal agreement, and now you have to enact the ‘get-out’ clause, is it? There’s no letter of resignation required.
You’re not even going out, so you don’t even have the displeasure (or pleasure, since you’ve come to your senses) of having to dump him.
That’s the thing about being the fall-back girl. He gave you NOTHING. So why do you owe him an explanation?
You don’t. You show him you are no longer his fall-back girl, and you do so thus:
Don’t be at his beck and call, every time there is drama in his life. Especially given it’s usually related to other girls.
Don’t answer every call from him, desperately wanting him to notice that it’s you who’s really there for him.
Don’t change your plans, or keep times free for him, just in case he can squeeze you into his busy schedule.
And don’t tell him. Start respecting yourself, being sure in your choices, and getting on with your life without worrying what he is thinking.
He’ll probably come to his senses and realise what he’s missing out on.
I’M PRAYING TO GOD that you remember HE’S NO GOOD when he does.
Or you’ll be back to square one. Because once he realises he can’t have you, he’ll probably want you. What you need to remember as that once he realises he can have you (again), he won’t want you (again).
I doubt I’m going to talk you out of giving it a go, if you get the chance. And who would I be to deny you your fantasy coming true?
But please remember that when he could have you, he didn’t want you. You need to expect that this will be the case again, and walk as soon as he’s back to treating you like his fall-back girl.
I wish there were more ‘ifs’ in that last sentence.