My pregnancy came unexpectedly amd i dont know who the dad is, help!?!?

ok so me and my bf have been having for about 8 months now weve had so many accidents of him nutting inside of me, and not one time did i get pregnant... untill i didnt start this month and took home pregnancy tests and all came back positive the thing is i kinda cheated on him with my ex we used protection but he kept saying it felt like he never had one on idk if it ripped or not but my ex n i have had about 4 or more times and i havent got with my bf.. i know i sound slutty but i really need help... i feel like its my ex's baby bcuz y now am i gettn prego whn the other times i didnt?? the very last time my ex and did it the condom ripped could this have happend earlier,???... and the last time my bf and i were 2ther we used unprotected but he didnt ***!!! now that i think of it.. my ex didnt put the condom on rite at one point it kept slipping off could this cause a pregnancy???? please help!!!!