so how do i play online

[tywald]

You can try use a VPN software like Hamachi, Tunngle, Evolve etc with your friend then one of you activate "Built-in ad hoc server" in PPSSPP and use the IP that the VPN has given you, if you are hosting the server then you use yours, if your friend is gonna host the ad hoc server then you both use his IP.

Configure firewall(s), disable fast memory(in some cases) and that's pretty much it.