My boyfriend has a large red/pink bump on his leg that is very painful and seems to be filled with a liquid or puss that's surrounded by a rash-ish looking thing. he has gotten it twice and it went away the first time before we could go to the doctors. is

This : This is difficult to answer without a clinical examination so i would see a dermatologist. Perhaps it is a boil or cyst? Read more about treatment options for cysts at the link below. I hope that helps!

Without : Without examining him, it's difficult to say exactly what the lesion is. It sounds as though your boyfriend could have a skin infection with abscesses or "boils". These usually start out as tender, red areas which become hard and then eventually develop a "head" of white pus. Once this drains, the area usually heals on its own. Most of these are caused by staphylococcus aureas, a common bacteria found on the skin. Occasionally, however, the can be caused by mrsa, the antibiotic resistent kind of staph bacteria. Next time your boyfriend develops one of these infections, start out by applying warm compresses to the area to help draw the infection out. Then, you should take him to his doctor so that they can drain it, test for what bacteria is causing it and be able to treat him appropriately - sometimes with antibiotics, sometimes just with drainage. If he ever develops fever, chills, or feels ill with this infection, call his doctor immediately. You can try and prevent these infections by practicing good hygiene and using anti-bacterial soaps. His doctor may have other suggestions for prevention. Good luck!