Well you certainly came to the right place with 2 JIZZ MASTERS in your presence! 
<aside>Ok, I've decided Floyd can run with me as Vice JIZZ MASTER. If he choses to oppose... I'm the incumbant, so I have a much better chance at taking the lead again and again!
</aside>
Anyway. First of all, you MUST stop your current masturbation mettod that work! I MEAN IT! It's not like I'm against diversity, but this will DEFINATELY cause problems in any future love-life that you may have! The thing is, you start when you're 14, and first get laid when you're 18 (standard l33t hax0r ages)... that means you've prbobably masturbated 1000 - 2000 times!
Here's my point... if you get used to a certain stimulation over the years thousands of times, your penis is going to freak-out when you've got a real vagina to cut into! BAD!
So here's what you gotta do... you need to change your method, and SOON. It'll take some practice... a little work... but in the end, it's going to be very important for you.
Laying on your back, with porn, lotion, full fist generally the closest you can get. Now about the flacidity issue...
Are you circumsised? That could make a small difference. Are you using lotion? Try with and without... some people prefer one or the other. Are you using porn? If you can't access it from your masterbatory perch, make sure you close your eyes and try to imagine some. You're not gay (I think) so staring/consentrating on your junk isn't going to help much. Alothough, some people enjoy watching themselves in the mirror. Give that a try! 
But here's the KEY issue! LISTEN UP! You have to stop using your current release method. If you can't get anything going, just stop, and try again tomorrow. Eventually if it's been 1 or 2 weeks since you've came, your penis will give in. It's like training a dog off canned food to kibbles. At first it resists, but then it get's hungry and just goes with the flow!
As far as technique... make sure you're not going too fast or too slow. My general recomendation is 140 beats per minutes (general tempo of a dance song).
Hope that helps! Let me know if everything cums out alright! 
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