how can I stop my foreskin splitting during penetrative intercourse?!

Two not very helpful answers to start with. Let's see if I can do better.
If the foreskin is too tight to comfortably retract, it just mean you might want to do some simple foreskin stretches in the privacy of your daily shower.
Follow the information in the links below and work the stretching into the shower routine. Let the warm water loosen and relax the skin before stretching. Stretches are to be firm, but gentle, with no pain. Pain is a damage indicator. Over stretching till it hurts can create micro tears in the skin opening that will heal over with non elastic scar tissue,....making retraction more difficult. No pain,...ever!!
There is nothing wrong with you. You have a naturally tight foreskin, just like every other intact (not circumcised) man on the planet had at your age. Over 85% of the males on earth are intact so you are on the winning side. The other 15% wish they still were.
Ignore the comment about getting circumcised. By the very nature of circumcision, it is a highly destructive procedure that unnecessarily removes 75% of the nerve rich, healthy, essential and normal, sexually sensitive tissue from the penis. How could letting some hack in a lab coat slice this skin off make things better? It can't and it won't.
Just work with the stretches and you will see some good results in two weeks, with full and painless retraction in 3-4 months. If it takes longer, just keep stretching.
What will happen is the Frenar Band (google it) of muscle that closes down the skin opening will relax and expand enough to allow the foreskin to glide effortlessly back and forth over the coronal ridge.
You do not need to retract fully to have sexual intercourse.
Do not listen to anyone who says you need to force the skin back to clean under there. Nature has this well in hand. The foreskin/glans combination produce a powerful anti microbial compund called Langerin. Langerin wards off bacteria and keeps this area clean and disease free,.....just like you are now,...so you know it works.
Go to: www.norm.org and read about the reason and function of the foreskin. You will see how very fortunate you are to still have yours, and how misguided are those who promote circumcision to validate their own sorry state.
Good luck with this
Mithras

http://www.norm.org/
http://www.fathermag.com/health/boy-care…
http://sites.google.com/site/circresearc…
http://www.network54.com/Forum/244184/

Ouch. Are you circumcised? Is the split around the penis just below the head or are you splitting your foreskin because it won't retract over your erection? I had the first problem, a friend had the 2nd. In my case, I made sure I washed morning and night and used some neo-sporin ointment. I tend to leak "pre-***" and it was accumulating under my foreskin and causing some irritation. Cleaning the area and the ointment helped. Im my friends case, he went to the doc who had him try some stretching of the foreskin, but he ended up being circumcised. Try to avoid that if you can, you will appreciate those nerves that get cut off later in life.

Personal experience.

If you haven't pulled your foreskin all the way back exposing the gland yet, then that may be the problem. If you have not done so yet, then you should pull it back a little each day under warm water until the foreskin is stretched and you can comfortably pull it all the way back exposing the gland completely.

Get circumsized. Your foreskin won't go over your penis.

I'm circumsized.

use lubricant, if it's a chronic problem and it makes sex difficult then you want to get a circumcision.

its normal. dipshit.