Twenty-two affirmations to trust it will get better — for the middle of something hard, when "this will pass" is impossible to feel.

Everyone knows that hard periods end. Knowing it and believing it are different, and in the middle of one the knowledge sits somewhere you cannot reach.
These twenty-two affirmations are written for that distance. Several of them concede the point up front — that you cannot see the better days yet — because a line that pretends otherwise gets rejected immediately.
Use your own history as the evidence. You have been through things that felt permanent and are not in them now. That is not optimism, it is a record, and it is the strongest argument available to you.
Then be careful with the timeline. "It will get better soon" invites disappointment on a schedule; "it will get better, even if it is unclear how or when" is the more honest version and the one that survives a slow month.

1. “I know that better days are ahead, even if I can't see them right now.”

2. “I am falling apart so I can be rebuilt stronger and better.”

3. “I trust that a better life awaits me.”

4. “I know that anything I lose is being replaced by something much better.”

5. “I allow things to fall apart and know that they'll come back together even better.”

6. “It's okay to feel overwhelmed. I will feel better soon.”

7. “Going through hard times makes me a better person.”

8. “I have faith that things are getting better, even if it's unclear how or when.”

9. “I feel my life changing for the better.”

10. “My failures have made me a better person.”

11. “I am allowed to make any change that makes me feel better.”

12. “I am confident that I will feel better with time.”

13. “I am allowed to want better things.”

14. “Every experience, good or bad, shapes me into a better person.”

15. “I trust that better, calmer days are just around the corner.”

16. “Even on the hard days, I know that there are better ones coming.”

17. “I am getting better but I'm good enough already.”

18. “I focus on ways I can help myself get better.”

19. “I am grateful for the things that leave my life and create room for better.”

20. “I am on the brink of something much better.”

21. “I know there are better days ahead of me.”

22. “Every breath I take brings me closer to feeling better.”
Then borrow the belief rather than manufacturing it. "Other people who felt this have come out of it" is easier to accept than a claim about your own future, and it is equally true.
Longer than you want and shorter than they feel, which is unhelpfully vague but genuinely how it goes. What is more reliable is that the intensity fluctuates — noticing the good hours is how you catch the turn.
Only if it comes with a requirement to feel fine now. These lines make room for the difficulty and point past it, which is a different move from insisting on a silver lining.
Sleep, other people, movement, and not making permanent decisions inside it. Affirmations help you hold the line while those do the work.