Pregnant and BF doesn't know yet

We were set on only having one child. I got the IUD put in cause I work messed up hours and couldn't remember to take the pill. (He doesn't want me to take the pill for this reason because I forget) Well it fell out, and I decided I didn't want it to be put back in cause I didn't know it fell out, I just went to check it to see if it was still there and it wasn't. I went back on the pill and did not tell him the IUD fell out and didn't tell him I started the pill. And I waited the amount of time to have sex like the dr told me before the pill became effective 

Well I just found out I'm pregnant again. I have been taking the pill 5 months and just found out I'm pregnant. 

Should I tell him the IUD fell out and I started the pill? I feel like he will blame me. I took the pill every single day so I'm not sure why it failed. I feel guilty