Most Helpful Guy
Do you love him?
What does he think about cheating?
Do you feel the need to make it again?
On my opinion if its a biological accident you shouldn't but if there are troubles on deep, you must.
Most Helpful Girls
No. You already live with the burden for lying to her everyday, why should you make your girlfriend sad too?
you dont need to tell, but you need to make decision. think again why you cheated. think who deserve you more. your girlfriend or your new one.
Oh boy. Unpopular opinion coming through: NO.
My reasoning depends a lot on your situation. Did you do it only once, or several times? If once, did you feel bad? (won't bother asking if you felt bad after multiple times, because that answer's obviously no in itself). Did you regret your actions, and feel overcome with remorse in a way that you just had to make amends?
If you genuinely feel sorry for what you've done, and if it's a one-time thing, then no, I wouldn't tell her. Think of it this way: humans have trouble keeping secrets because things wear on our brains. It's easier to tell someone about our problems because we are sharing in our misery, creating a camaraderie with someone through our pain. Whatever guilt you may feel would be easily alleviated by telling your partner, but then they would have to know and suffer heartbreak. Again, assuming it was a once time thing and you really feel bad and want to make up for it, why would you want to hurt that person in such a way?
Granted, some people might say it's worse if your girlfriend hears it from someone else. Personally, if my boyfriend cheated on me once, felt awful, and resolved not to tell me to spare me from heartbreak, only for me to find out later from someone else... well, I think I'd appreciate it more than if he flat out told me. It'd hurt, sure, and my trust would be shattered--but he would be showing me that he cared enough about my own happiness to refrain from telling me. Keep in mind, I'm not promoting hiding an affair from your S. O.--I'm saying that, if you do it ONCE and TRULY feel guilty/repentant for your actions, it is better for you to keep that pain to yourself, because telling your S. O. is only going to plant the seeds of doubt, ruin your relationship, and hurt everyone involved. If you keep it to yourself, however, you alone maintain the burden of remembering what you did. You suffer in silence for your actions, while your S. O. remains blissfully unaware. Essentially, you are paying for what you did without bringing down the other person.
So no, I don't think you should tell your girlfriend, assuming it was a one-time thing and you truly feel guilty. However. If you did it more than once, and/or feel little to no guilt for the act, I would tell your S. O., because it is clear that you don't care enough about them to continue a monogamous relationship with only them, to devote your time and love only to them, and they deserve better.