2.5 years is a long time to be working on something with no tangible result that is bringing in money. Of course, I don't know what sort of product you're working on, but it is possible that you've simply picked something that will take too many man-hours to build for the size of your team.

I've launched my own products before, and they're usually something I can finish in 2-3 months working full-time with a part-time designer. If you only have weekends and holidays, even one of those could take as much as a year, if not more.

The only thing that is going to get you excited again is to get some tangible result from your work. Try to simplify the product down to a small prototype you can test on your target market. It doesn't even need to be an app. It could be an Invision or a 'fake' app that shows the navigation and what your app could do.

Get some people together and show them your prototype. Get feedback. Improve upon it.

If they really like what you're doing, it might give you a sense that you're on the right track. You need shorter feedback cycles to get energized about these sorts of things. That's my experience, at least.