Yeah no give it back and move on, to have those important conversations and for them not to be remembered is not okay. I understand forgetting, but if he really cared he would have written them down or something. My bf had a notes tab on his phone so he wouldn’t forget things, it’s not hard, it’s not caring on a level that is beneficial to you.
So actually leave him because all it costs to make that a truly special moment is time and effort. Even if he couldn’t accomplish what you wanted (don’t have enough context on that to know how able he is to do it) he could’ve AT LEAST spent time with you, taken you on a walk, worn clothes. Basically anything else. And ALSO a year and a half is plenty of time and warning to save up for and plan for what you wanted. There’s no scenario in this where he’s in the right.