http://www.steadyhealth.com/masterba...x_t120068.html
The men on here all say not masterbating helped them to be able to cum. Maybe lay off the palm shining for a while ?
I googled " masterbate too much can't ejaculate during sex " and founds tons of forums and topics.
It seems the answer is to NOT think about ejaculating but rather the sensations while having sex. Masterbating less and changing your technique to a slower less pressure grip..
Hope this helps!