When you use your hand to masturbate you can (without really noticing it) lose your erection and stilll get off! When you are inside a woman you wont get enough friction to have pleasure for yourself or for your woman. For real penetrative sex, you need a full firm erection. A big problem with jerking off is that you condition yourself to ejaculating with a semi! The FleshLight is great for this problem. It doesnt feel like a real pussy (nor does it smell like one) but it feels pretty damn good. You lube it up..lube yuor penis up..and make love to it...it gets your body used to having an orgasm by thrusting into something instead of jerking yourself off! It simulates real sex!
Fleshlight is definitely better than using your hand and probably the closest thing to a real pussy. Because you can't use death grip on your dick and super fast motion gets difficult if you are trying to fuck that thing and don't jerk off with it. I also read that it can help with PE.
Just google after fleshlight and PE a bit, you should find some reviews how guys improved their stamina. I don't know if it really works, but maybe some guys can profit from that.
