Are you planning to drop the project soon? It just seems like you don't like working on it anymore. As much as I would love to see the finished version, you shouldn't force yourself to do something you don't want to do. Especially something that could potentially take years to finish.
If that's not the case I apologize for bringing it up. I understand it can be hard to get motivated sometimes. Alternatively, you might consider finding someone to help you work on it if it's just too much for one person.