Is This Normal?

My boyfriend's friend is in a, like, four/eight (tbh I have no clue how long they've been together) year relationship. They're engaged (and have been for a year or two). But, like, every other month they fight and he sleeps over at our house. So I'm wondering, is it normal to fight that much and that extremely? Do I have that to look forward to? I've never been in, like, a relationship lasting more than a year and never lived with a boyfriend before now.