@Honeycat, if you cannot wean yourself from having sex with him, I would consider taking Prep. Basically, view him as a high risk partner, as someone who can transmit HIV to you.

From the website of CDC: "Pre-exposure prophylaxis (or PrEP) is medicine taken to prevent getting HIV. PrEP is highly effective for preventing HIV when taken as prescribed. PrEP reduces the risk of getting HIV from sex by about 99%." When I was in New York city last year, there were public service advertisements for PrEP inside trains.

This is medication you will need to take faithfully every day. Your local Planned Parenthood should be able to put you on it. Note that it won't help prevent the spread of other dangerous STI's including hepatitis.

And whether you are able to detach, do go to a doctor or Planned Parenthood and get the full battery of STI tests right now.