Ok so.. i can only cum when i touch myself .. like if a guy is fingering me or eating me out i have alot of little ones but never the big bang =] and when i have sex its the same.. but when i masterbate [with or in front of someone]
Give in-depth instruction to your partner. Show him or her how you do it and then guide them when they do it to you. Then learn to relax and enjoy it, not worrying about whether it happens or not.