My guess is the pregnancy is the key-but exactly how, I'm not sure.
1)They are about to pick up their lives and move to a new area of the country.
2) She's just found out she's pregnant
3) She has no job and it's hard to get a job in a new area, especially when pregnant
4)He has no job, no scholarship, no school, no future career -- everything i s alie
5)She confronts her husband about all these things
6)The argue
7)It get's out of hand
8)He kills her.