Simply stated, if you can stimulate yourself to have a cllmax when alone,then teach your boyfriend exactly how to do it. If you can't do it all by yourself, your body may not be ready quite yet.
Remember to use plenty of lubrication...don't do it dry. Pee right before you start, take your time, try to relax, don't worry about it and just enjoy the pleasure...it will come when everything is right.
Let us know if it works.