I cannot have sex with my boyfriend, his penis is only 3 inches and does not reach into my vagina. what caused it to be small? testes are normal.

Small penis: If everything else about your boyfriend is normal - testicles, hair distribution, height, etc - the cause usually is low testosterone levels in the later part of pregnancy that he was exposed to. It happened a long time ago. There are surgeries to correct this problem, but unfortunately they are not always successful. A urologist could give him whatever options there would be.