I don’t think you can do any physical harm to yourself, unless the clothes you speak of are jeans and then you might cause some irritation to your genitals by pressing your jeans, which are generally rough, against the skin. So on the one hand, you can continue masturbating the way you are for as long as you like. However, there’s nothing wrong with actually touching your vagina directly with your hand. You may feel like doing that would make masturbation more “dirty” but masturbation is masturbation and since it will feel better with your hand, and since you want to get used to having a partner touch you, I’d recommend at least trying. If you end up getting hooked on your method of masturbation, if psychologically you can only have an orgasm when rubbing yourself through clothing, that could cause you problems later on. It probably won’t, but it could, so at least from time to time you should try touching yourself without any clothes on.