Losing interest in sex can make the penis lose its hardness and hence when you are with a person, you must think of the pleasure you are getting and not concenterate on the time you are taking. Of course, if you cannot ejaculate, there is nothing harmful, but it should not become a habit. such dry humping is common in youth who are known to be detached from their partners and are having sex only to show their virility. They "perform". This may work well in some industires like porn, but it may become a habit and create problems when one wants such intravaginal semen ejaculation say for having a baby or to make the lady feel the completeness of the act