the chances of HIV passing though oral sex are extrememly rare. there havn't been any documentated cases that say 100% that HIV was transfered orally. i dont know what your husbands sexual history is, but my ears perked up when i saw HIV in the post name. I am HIV+ so if you have any questions, or do test positive, let me know. HIV is most commonly passed to the receptive parter (either the woman, or with two men, the bottom) it can go the other way but it is more difficult.
everyone who is sexually active should be tested at least once a year regardless if you are in a "loving" and "monogamous" relationship. in all honesty, a lot of people i've come in contact with who have HIV are people who were in a relationship and his or her partner cheated. this isn't to say that you dont trust your partner, but it just should become habbit for your well being.
here are some really great sites for more info on HIV. http://www.HIV.com
this site is great for general info, and is helpful when you first test positive. http://www.thebody.com
this is a really in-depth site about anything HIV related. it can be overwhelming to anyone who is not familiar with terms and processes. it is data heavy, and although you can find answers to simplier questions, its easier to navigate the other site. this site however, has a cool thing where you can "ask the experts" so you can get specific info on your case which is nice.
if you guys want more info. let me know