I'm going to end a 10-year friendship
Wow, why end the friendship?
He was only helping me because he thought I would help him in the future.
If he was just using you, then ending this "friendship" is the right move. Such "friends" will abandon you the second they think they can't get anything else out of you.
Wow, I'm glad you think so. I've been suspecting this for a long time.
Yeah it can be really hurtful to invest so much and find this out. I think you should tell them and not ghost them about how you feel before you leave.