DUDE - stop what you are doing, get on your knees and give thanks to whatever god you pray to.
You have found yourself a gusher - one of the greatest things in the history of sex. Seriously. There are many men that have never experienced a gusher. You are lucky my friend. Sure, it makes for some major clean-up after sex, but it is WELL worth it. Men are visual responders - seeing and feeling that rush of cum is the greatest feeling in the world.
Congrats. Learn to love it cause it's a great thing and it means you are doing something right.