why do men cheat?

ka

My younger brother and his girlfriend are both 20 and she’s 10 weeks pregnant. they’ve been together a little over a year and she has just found out a few days ago that he got nudes from his ex. tonight, she found his “other” snapchat and figured out how to log in. there are HUNDREDS of girls on there that he has been talking to the whole time that they have been together, i’m absolutely heartbroken for he, my whole family loves her and she’s perfect for him. they have always seemed so perfect and so in love and he’s saying he’s gonna go crazy without her. i do not and will ever understand why men do the things they do. i’m so sad for her :(