How is it possible for the second baby’s chromosomes to be different from the first baby’s chromosomes?

Structural changes can occur during the formation of egg or sperm cells, in early fetal development, or in any cell after birth. Pieces of DNA can be rearranged within one chromosome or transferred between two or more chromosomes.

if your boyfriend is cheating on you, my best advice to you is to dump him, he's only going to drag you down. and if you do, don't fret there's plenty better that know how to treat a person right. i mean honestly, the whole point of a romantic relationship is love, and if you love someone you aren't going to cheat on them. i do believe in second chances, but why would he cheat in the first place? i personally feel that if someone cheats, they ruin any chance they wanted/had with you. i wish you the best of luck with this, hang in there.