I've never been able to wear tanks or bathing suits or anything that may show my underarms. I've tried so many things to try to lighten the skin but nothing works. My husband has never even saw it. Ruins my life during summer, and also during sex, because I'm always afraid someone will see it our my husband will see during sex and be disgusted. It's ALWAYS been there. Please help!

I just watched a show on The Doctors yesterday about this. She had dark spots under her arms and showing around the sides too. They sent the woman to a spa where she received treatment that was all natural and mainly consisted of softening creams followed by volcanic ash exfoliates followed by lemon juice and more creams, made of things like real lavender and grapeseed oil and such.
It is very common to have dark skin in the folds and hidden parts of the body. Most of us have some variation on this, such as between the thighs.
I am concerned that you feel that you have to shrink from your husband though! Tell him that it's common. Somehow I doubt that he is going to be as disgusted as you are. Maybe even see a therapist about this.

I have the same problem and have been using Dove Cleartone deodorant which has cleared up most of the darkness. Exfoliate under your arms in the shower with a lofah or bath puff. When shaving your armpits, don't go over the area many times with the razor. Two or three strokes should be enough without irritating the skin. Apply the deodorant after your shower. You can find it at the drugstore or online, but if you can't find the Dove one try looking for Nivea deodorant which is the same thing.

Dark underarms may be due to hormonal failure in the body. If cosmetics are not helping, or other useful tips (for example here: Ways How to Get Rid of Dark Underarms. Wear Sleeveless Clothes Again.) You need to go to the doctor, he can tell the cause and resolve the issue