Hi Henry,
If you feel "stuck", I challenge you to see your situation from a different angle.
You own a property in an area with consistent growth and property appreciation. You're able to cover nearly 60% of your mortgage with income from tenants. You then split the remaining balance with your girlfriend. By doing this, you're able to save cash while generating income on an appreciating asset. You are not "stuck" you are in the midst of growth.
If you want to grow your real estate portfolio more quickly, continue to save cash because it is truly king. While doing that, research multi-unit properties with good cash-flow and lower purchase prices in other states. Using the forums on BP, I'm sure you'll quickly identify a few good cities to consider.
Remember, you chose a long-term strategy and your current process is working! Instead of being discouraged by it, recognize your success and apply that knowledge to your next project.