Anytime "fear" leads you to something, there will be anxiety. Condoms do decrease desensitivity but there various sizes to work with if they feel too tight. Try them all out to familiarize yourself. Explore other avenues of sex other than penetration....safer methods. Work up to penetration with your partner. All these will allay the anxiety factor which will decrease the erectile problem, I would think.
No, excessive masturbation should not necessarily lead to problems with achieving and maintaining an erection - and who says masturbating every day is excessive anyway? :)
Do you have problems with your erections when masturbating, or only when attempting penetrative sex? If the latter, perhaps your fear of HIV is causing anxiety that is affecting your ability to maintain an erection (as that anxiety won't be there when you masturbate)?