Masturbation should not decrease your testosterone levels and in fact masturbating often should help to increase your testosterone levels.
When you masturbate you lower your androgen receptors in your brain and when your androgen receptors are lowered you produce more testosterone.
Masturbation is also very health for you and may even prevent testicle cancer and can even help you become more fertile as well.
Masturbation has a host of health benefits such as relieving stress and tension, boost your mood, alleviates pain, helps improve concentration, helps you sleep better etc.
Masturbation also feels really good and there's nothing to be ashamed about as long as you do it behind closed doors where nobody can see you.
Even using a vibrator on your penis is also good to help get you to ejaculate without having to get your hands dirty etc.