The sentence "I will cherish forever" is a correct and usable sentence in written English. You can use it when expressing strong and lasting feelings for something or someone. For example, "This friendship was forged in childhood, and I will cherish it forever.".
"This is just a day and a moment that I will cherish forever.
"I want this to be a celebration of my time at the club; a memory the fans can take home and one I will cherish forever".
"It is a moment I will cherish forever.
That was my moment I will cherish forever.
To be in the same category as them is something I'll cherish forever.
It's been a good game for me [he also dismissed Kevin Pietersen] and it's something I'll cherish forever".
That's the memory I'll cherish forever.
Awesome tool! I started using it one year ago and I never had to look for another app
Ha Thuy Vy
MA of Applied Linguistic, Maquarie University, Australia