You can get married and start the process.
1) It may be easier for him to visit you and marry at which time you can get some joint accounts setup. He returns to the UK prior to the visa/ ESTA expiring.
2) You can marry in the UK but that does require a special UK visa on your part
3) you can marry any where else that you can.
4) you can marry online but can't file until you have actually met. (options 1 to 3 are better in my opinion.)
Once you have married you can file and then find either a way to increase your earnings or obtain an Joint Sponsor or both.