please please please someone help me

i really really messed up. i was with my ex for a year and a half and we broke up last september but we constantly talked and saw each other for the past 5 months but he treated me so badly during those months always pushing me away and kissed to girls while i was at the same party on nye. two weeks ago we decided to take a break of talking to see if he wants to get back together and i started to feel ok without him. then i started spending the night at a frat house for my best friends boyfriend is the ex president and they didn’t want me to go home alone drunk so i ended up sleeping in the same bed as the current president of the frat but we didn’t do anything. my ex spam called me 27 times the second night and called me a whore and other stuff for being there. mind you i respect my body and i lost my virginity to him after 8 months of being together. i got so mad that he called me that that the next night i was over in the presidents room again and we ended up making out. the next day my ex came by and was begging to talk and he was crying because he realized how badly he treated me and he finally wanted me back. but i was still so angry and the past 5 months and what he said two nights before that i wouldn’t let him in. then on thursday i ended back up at the frat house and i ended up sleeping with the president because he was genuinely so sweet and trust me he kept making sure i was ok with it. but the next night i got home from drinking with my friends and that day i found out some shit about my family and it sent me into a spiral and my suicidal thoughts came back. i live alone and i texted my ex because he used to help calm me down (i have had severe depression for 3 years and he knew exactly how to help me) and he knocked on my door and immediately hugged me and took me to my bed and just laid and put cuddles me and calmed me down. he asked later that night if i had kissed anyone and i said yes and he flipped out and left punching the wall on his way out and broke his mirror when he got home out of pure frustration that he did that to me and let me go for so long. then he came over again last night without any warning and fuck dude i want him back and he wants me back and he apologized for absolutely everything he has done to me but i wouldnt let us have sex. he ended up getting a panic attack because knew something was wrong. i don’t know what to do because now i want to get back together but if i tell him that i slept with someone else he will absolutely never speak to me again but i also can’t live with the guilt of hiding that from him. i truly don’t know what to don