After being dumped by his longtime girlfriend, a man who believes in eternal love asks for a second chance and they are given the magical opportunity to start from the beginning with what they know today and do better.

I want them to have to chose what knowledge and memories they need to be good for one another, and what they really need to never have done or said.. Some things should never have happened. They need to make the choices together and deliberately wipe away experiences.

Thank you! Of course.. there ought to be a rival.. I have to ponder on that for a while. :)

Thank you! I am glad you liked the idea - and thanx for super advice! :)

>>>When his girlfriend wants to leave him

Rather: she leaves him. Period. Full stop.

New paragraph: Characters do not merely want. They do .

And she leaves him for another guy, too. Give him a rival. That is a stronger inciting incident. It creates more tension, makes his struggle to win her back harder.

What rabbit do you plan to pull out of the hat of the plot to make it possible? What's the magical gimmick?

Very cool, don’t we all wish we had this do-over chance 😉. Getting an “About Time & Click” movie vibe from this.
1. Most of these shows focus on the complications of time travel and have to come up with some unique method of how the time travel can occur which I am not seeing in your logline. This will give focus to your magical opportunity and the stakes.
2. Think about amping up your inciting incident e.g. “After being dumped by his longtime girlfriend, …” but make this your own, many loglines start like this - you get the idea. One way to keep the reader curious when constructing your logline is to have them questioning - how is he going to keep this reluctant girlfriend from saying “check, please” at any given moment?

Take care.