Should i get back with my ex boyfriend who had with my cousin?

so heres the story.... me and my ex started having problems we were jusst not putting things in place so we dicede it to take some time off.. we didnt really talk as much but we kept in contact.. then rumors started going around that him and my cousin had i couldnt believe it my own cousin and my first omg! i was so hurt that i didnt even gave him a change to tell me his side... i did speak to my cousin about it and she dinided it at first but after she admitted.. well point is i never spoke to any of them again... so a week ago i bumped into him and he told me he wanted to talk to clear a couple of things out so i gave him the oppotunity to speak. so he spoke first he asked how was i doing and and i said just fine and he started saying well i want to clear my name i know u think i had with your cousin but is not like that i have always tried to explain the truth but you never gave me a chance... i want you to know that i still love ua nd i cant stop thinking of u.. i was chocked i didnt expect that so i told him that i need it some time to starighten up my mind and to make sure wht i wanted.. i dont know what to believe i do love him and i always will.. i dont know why i didnt do anything about it i could of fought for what was mine or i could of listen buti was stupid.. what should i do?? in a way i do believe something happend between them but i know my cousin doesnt care about me and she doesnt respect her self so why should i think she will respect me!! she is promiscuous and i cant expect that from her but i need advice please help!