Sorry I hate this way of writing but!
Person 1 and person 2 have a child together. Terrible relationship, break up after person 2 leaves person 1 for someone else. That fizzles out. They hook up.
Person 2 meets new gf. Person 1 is angry because she is left to one side again. Two years later person 2 is having another baby. Person 1 tells someone (person 3, vague friends with person 2) that they'd been sleeping with person 2 off and on for the whole two years.
Person 1 has always been resentful and petty but usually honest. They have texts to prove the affair. Could texts be fabricated? Person 2 was caught with topless photos of person 1 which he replied to saying 'nice'. I know who I believe.
Who's lying?