Should I leave my startup?

This is a throwaway account as I'm pretty active on HN along with my partner.

I've been running a startup on the east coast with my co-founder for about a year and a half with only a third of that as serious time as we both had other commitments.

We are a tech/non-tech partnership, myself being the tech side. As such, I've built pretty much all of our software and website.

I think we do some pretty cool stuff, and we have customers that agree. However, I'm getting strong urges to move on.

For starters, I'm not having fun working on this company anymore. Our backend is temperamental and I feel like the workload I have is large enough that it's difficult to stay on top of everything. I also don't feel like our team or environment is fostering creativity and energy. I have little to no motivation anymore and I'm not excited about the product or even getting up in the morning to go work on it. I feel like my co-founder is talks down to me, lectures me, and is extremely stubborn. He does his part though, so I'm not complaining about that.

I believe the company could go somewhere, and it already has a bit. However, growth is extremely slow (read: I won't be making a real salary any time soon) and I wonder where we would be with a different team that had better energy, creativity, and synergy where new ideas were more willing to be explored or even just considered without making the idea-maker feel put down for bringing it up.

I've had some new opportunities present themselves that I can't get out of my head. Opportunities with teams that seem far more energetic and fun and will push me to improve. I want to surround myself with smart programmers that will make me a better one. Right now I'm very much on my own and I'm getting tired of that. On top of that, I have a strong urge to start making money and building some savings.

With this company (as with most I'm sure), there is a constant "what if?" What if I just stay a few more months? Could that big break be right around the corner? What if I'm not giving this company enough time to see where it goes? What if I don't jump on the opportunities elsewhere, what would I be missing out on?

This startup has been great for my career and personal development and I don't regret it one bit, but I want to move on.

Any advice? Thoughts about how I should leave (it's 50/50 ownership right now) would help too.

Thanks.