should i lie????

I found out i'm pregnant but i think it's another guys baby instead of my boyfriends.. i cheated on him last month (i know i'm a horrible person and i deserve to die) should i just lie and say that it's his baby for 9months and then tell him when i'm 9momths pregnant that it's not his?? i don't know what to do i don't want to lose my boyfriend over this.