The best cure for depression is taking action.
First of all you need to (put things in perspective). A failed relationship is not the end of the world! Close to 50% of all marriages end in divorce. You can well imagine how many non-marriage relationships fail to last. Therefore you are not alone.
Secondly you have to decide if simply "talking to another girl" considered cheating in your book. You are entitled to have your own "deal breakers". However most people require a little more than talking/befriending someone of the opposite sex to end a relationship with someone they are "in love" with. Remember you get to choose who you spend your time with. Thus far it was (YOUR choice to move out) of your house. Where you go or what you do from there once again is up to YOU.
People only panic when they don't have options or they lack the emotionally security that comes with having family, friends, and co-workers that care about them. Since you are living with your dad apparently you have someone you can count on. The next step is to work on you. Strive to get a good job which will provide you enough income to have a place of your own.
If you suspect your boyfriend was doing more than "talking" to another girl then move on. LIfe goes on. With over 7 Billion people on the planet the odds are in your favor you will meet someone that shares your same values and thinks you're special. For additional advice on getting over a breakup feel free to read my hub. Best of luck! http://hubpages.com/relationships/Getting-Over-The...