2 words: Butt plug.
Get yourself a decent sized butt plug... not one too big around as that will just be foolish. Lube it and yourself up real good, then slide it in (it may take some doing, but persevere...). You can even have your BF help you by fingering your hole and helping you relax before SLOWLY working it in you. Once the widest part is in, your sphincter will close down on the narrower part that follows, and you can actually keep it in you, under clothes if need be, for quite some time. You might try putting your butt plug in an hour or so before you plan on getting fucked. That will help stretch your sphincter by keeping it open (though clamped around the base of the thing).
Then when it's time to fuck, your BF can help extract the butt plug. Don't just pull it out, play a bit with removing it. Turn it into a sex game. Once it is out, have your BF lube himself up and enter you. The job should be easier, especially as time goes on, and soon you won't even need the butt plug anymore.
You can also try getting a set of anal beads -- not the little ones (those are for girls and wimps IMHO), but the ones that are about 2 inches in diameter. Have him insert them into you (lubed up, of course), and then slowly pull them back out. I am told the sensation is wonderful, and again, will help open your sphincter to accommodate him.
I know you said you wouldn't do them, but it bears saying: A word on poppers... they have been linked to HIV infections, not because they contain HIV, but because of how they lower the body's immune system response to infection. They are also linked to Kaposi's Sarcoma (KS) which often manifests itself in HIV+Positive people. They are made of carcinogenic chemicals that really aren't good for you or your brain in the long run. If you can get ahold of medical Amyl Nitrate (used for treating heart patients) that is somewhat better. The effects are milder, not so harsh. Over the years, the FDA has had various forms of poppers recalled, insisted they be reformulated and relabeled, etc. They used to be a close relative of the medical Amyl, called Butyl Nitrate, but now, god knows what's in them. And they are a danger to use if you're on any ED medication like Viagra. If you think you need to relax with the help of some kind of chemical, stick with a nice glass or two of wine and let the alcohol do its magic. You'll kill off fewer brain cells as well.
Attached are a few pics of butt plugs and anal balls for you to see. One of the butt plugs has a bulb attached so it can be inflated to help stretch your hole. <wink> I hope they help.
BBJ