Never. I can see where people could rationalize, "well I am lubing it up for her". But theres the problem, if she needs a dildo that just means you are insufficient. (Aka your dick isnt enough for her)
I have prided myself on a sexual experience that isnt greedy. Many men only strive for their own orgasm, I always hold off until I am sure my own partner has been pleasured. If you dont have amazing sexual stamina, you can always learn to finger for the g-spot, or learn proper oral.
I've put my all into it for my sexual career and I have a pretty high approval rating. Many women say that no ones even gives them oral and several have told me I'm the best they've ever had.
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"Why is ontology so expensive?" - JH [Is this live?][Joyless planet...]