Confusion of paternity

Sorry for the rant but long story short i was in a 4 yr relationship with my now ex / father of my son we split up about a month and half ago and in the midst of my lusting 2 weeks ago I met this guy and we had sex yes I know pretty stupid of myself but I missed my period which is now 12 days late and decided let me test bc since I am exclusively breastfeeding my 11 month old my periods just be everywhere but I tested 2 days ago and it was positive and now I am unsure of who's the father is I am rooting big high possibilitie with my ex he's the K and the other guy is the L.. and my ex he did the pull out method cause I've seen I know not 100% effective neither and the other guy said he never came which I never saw him do which is odd