Apart from the STD or pregnancy spreadings (let's take away that for a moment), why do some people get so emotionally to the point of not eating, depressed for days, or develop trusting issues if they weren't even engaged to that person.
I can understand if it's a fiance(e) you're planning on living with, sharing income taxes and even forming a family after getting married but a boyfriend/girlfriend??
First, if it's only a relationship there was nothing other than feelings bonding you to that person. What I meant by nothing is financial cost, a house, payments, children, etc.
Second, you can break up at anytime if you're only dating but it'll be very difficult once married or if you had the marriage date, already bought the house, ring, etc.... only to have this happening to you.
Third, I know cheating is still wrong either way but it isn't as devastating as betrayal after a marriage. If they cheat while on your relationship, so what? You might take your anger and energy yelling at them or sending them to hell, telling them it's over but once it's over with, it's done... easily (unlike in marriages, you would need to file for divorce, get a lawyer, etc.).