Can yous help?(don’t judge)

Hey guys!! Just need a quick question as I kinda fked up! Please don’t judge... My last period was in the 13th august.. I slept with a guy on the 22nd and got back with my ex on 24th and was with him up until the the beginning of September, slept with each other quite a lot and he came in me bout 4/5 times (he always cums in me and I never fall pregnant so I didn’t think of anything stupid I know!!) and on the 12september I found out i was pregnant test said I conceived 2-3weeks ago)..( I text the guy from the 22nd night and told him and he told me it definitely isn’t his he didn’t cum inside me) and I know my ex did on the 24th and a couple of times after that ... but I’m still confused as to who the dad could be ? :( what do yous think