<human>: Can anyone tell me why "cheating" is considered bad? I (F/26) have been in an ongoing relationship with someone I care about very dearly (F/22), but we never said we don't want the other person to sleep with other people. I recently moved across the country from this person, and slept with someone else - and when it came up (I thought casually) in conversation she told me she's "done with" me and hung up aaaand now won't answer her phone/respond to messages.

I am highly confused. If she had told me not to sleep with other people, I never would have done it - however, she never told me not to (in fact, she informed me on several occasions I'm not her girlfriend because labels are lame)! Why is faithfulness the default? Why do I not understand this? I would never get mad at her for being with someone else unless we explicitly agreed not to be with other people. Help me, Reddit! (not sure if this is at all important, but was raped as a youngin' and my therapist thinks maybe that made me conceptualize sex as something that's not meaningful)

Can you summarize the given text in a few sentences?
<bot>: Don't wanna give her up but apparently i let her down. I ran around and that makes her feel I deserted her?!