The above advice quite comprehensive and practical. You can add fast breathing when you reach orgasm. Slow breathing lengthens intercourse time, fast breathing quickens orgasm.
Hi,
Are you saying that you are losing sensitivity? If so, there are a few things that you can try to help with increasing sensitivity. Skip masturbation for a few days before you see your girlfriend, in order to allow the nerves in your penis time to recuperate and become more sensitive. When you do actually engage in sex, try different positions to figure out which position increases your sensitivity. It might help to have your girlfriend climax first, before you do. There are penis creams available (you can google for more info.) that help restore penis sensitivity; you might consider using a natural topical cream. Lastly, you could always seek advice from your doctor to see if this has to do with nerve damage or a circulation issue...
Good Luck