How do I tell him

I was having a party at my house abt a month ago and my boyfriend left to the store to go get munchies. I was black out drunk n only found out last Saturday I was raped b.c the culprit wanted to basically brag it off to my boyfriend's dad. So rewind to abt 2 weeks ago, I missed my period n took a pregnancy test and bam it's positive. I was super excited cuz me and my boyfriend have been trying for a couple months to conceive prior. But now I'm scared to tell him abt what happened cuz I still dnt know exactly what happened. But this other guy is now thinking I'm pregnant with HIS kid....after he tried tell me he dnt have sex without a condom. I'm just so confused and scared right now. I dnt know what to do. Any ideas?