if her bf is narcissistic it will be hard for her to breakup.

first u should ask if they already have alot of sex. if yes, then she is a roti girl which means anyone with little emotional or money investment can bang her without marrying. girls who already have plenty of sex with their bf/husband and still not loyal to them will just do the same when they meet better guy.
if she is a good girl and upkeep her price (not giving sex easily without marriage commitment), then worth to go for.

after you have alot of sex u know actual point of sex is just to make baby, and real satisfaction come from having children and growing them, and with wife / children that are loyal and sincere to you.

those who just enjoy sex only for sake of sex will never understand this, and thats why in this world so many orphans, single mum/dad, divorce etc because apparently children are by-products of their sex, and not main product.

if everyone treats children as their main product of sexual act, there wont be so much evil in this world.