Cheating pregnant gf

12week along gf was late. Walked in on another man in her bed this morning. I just walked out. I can’t tell u what I’m feeling but it’s not good. Idk if it’s even my kid now. I feel empty. Made this post in cheating stories but I was told this is the place too be. Anyone ever been through something like this. I’d appreciate dms on here how to manage this in the best possible manner