Is this really my fault? please advice. i m hurt?

details are>> I was k friends with my ex-ofcourse feelings still involved..before i left for vacation. Before I had left i had thought of totally let go and heal with my family. I was doing well. I left my apt keys with him, so that he could look after my mail...plants and use the internet if he would like..coz he is not in a great room-mate situation himself. Btw i was gone for 6 weeks. he missed me tremendously and wrote me in email."that he misses me. he wants to make things work, he want to show it the whole world, he love me so much". I belived it. i come back. few days went by nice and sweet. i go thru his phone bill. the day he had send me all those nice emails, he was actually talking to several different women..and he had his profile up in yahoo personals. i felt hurt...and now he is saying that i m looking for things to fight. I m so hurt again. that i have crying whole day today. and he sees nothing wrong in it..that he was actually sending me wrong msgs. please help.