Please no judgment ..

I've messed up ! It's a messy situation where I've been with my boyfriend for 5 years around the end of August we been trying to convince but it never happen and we broke up out of spit in The end of December ... December 31st I went out and met up with an ex being drunk and dumb on New Year's eve and my  period had just ended .. So it ended up being a one night stand .. He says he didn't bust in me and when we were together he would bust in me and I would never get pregnant ... But I got back with my boyfriend and we continued to try I'm three days late and tested postive today ! Any possible way it could be the one night stands ?