So you are 14 years old hon. This is no way to start out your dating life. Boys who lie aren't worth your time. If you were kind enough to forgive him for being with another girl (your friend especially---- and boy, some friend! I might add) and then he comes back and isn't working hard to make it up to you, well---------- he's not worth having.
I do want to say that relationships build. You date for a while casually. I know when you are in highschool that is a hard thing to do---- it goes straight from "i like you" to we are boyfriend/girlfriend. As you get older--- you usually get to know someone through dates. Spend time together and see if there is something there to pursue. You could date others if you want to as there is no commitment early on in dating. You try not to be sexual with them at first because then it makes the relationship more serious right off the bat. You can have the hots for someone and they you and maybe kiss and know that you are attracted for many dates and let the rest of your pysical contact build. Then after you have been together for a while and BOTH are sure that you really really like each other, you can decide to be a couple. Then as you are a couple, you get more and more serious as time goes on. I just wanted to tell you this as understanding the healthy progression of a relationship might be good to keep it all in perspective.
Back to the subject in hand--- if you are having to ask "is he cheating" and "how can I keep this going" after a month------ the relationship is not solid.
Find a boy that treats you like a princess. Fight the urge to be attracted to relationships that are such work and guys that you have to "win" and "keep". good luck
Agree with Kayannaboo.
Cheater without therapy or help= Cheater continuing to lie and cheat.
Let the other girl have him; all she is getting is a boatload of drama, problems and heartache. Not to mention the risk of STDs/STIs.
Want better for yourself dear. I think you deserve better, but most importantly, you have to BELIEVE you deserve better.
He deceived you once and so that makes him a deceiver. Men have a way of playing with out heads, they are very convincing indeed and the fact that we want to believe them makes it so much worse. He has proven himself to be a cheater, why would you believe otherwise? And the fact that both of you have only been going a month, he may not feel as if he is committed to you. This guy simply wants to have his cake and eat it too. Do not count this girl as dishonest, you are already suspicious of him and what has he done to make you believe that he is truthful?
My suggestion to you is not to get yourself entangled with a moron. Simple. Do not set yourself up for disaster and a broken heart. You sound pretty young and so I will say that this isn't something you need right now.
Good luck and take care!