I finally got a loving girlfriend but still have temptations to flirt
How could you? Is there something wrong with your girlfriend? Does she have some kind of flaws?
I am the one to blame, I find that man irresistible.
It will probably hurt your girlfriend's feelings if you flirt. You may upset her and make her feel that you are looking for a new partner. She might even break up with you.
She doesn't need to know. I trust her and it will be a calm affair.
I believe it's best that she does know, because honesty is key to a healthy relationship. How would she feel if she found out you were being unfaithful, herself? Why not come clean, she will appreciate your regret to this.