Looking for some advice fellas and looking for your opinion on the following questions

>is it okay to flirt with other women?

>is it possible to stop noticing other women?

>are sexual desires for other women normal and how do you deal with them in a relationship?

>is no fap the answer?

for anyone willing to offer help:
>girl interested in me
>already have gf
>girl flirts with me
>see girl come into my work a few times and flirt back
>nothing physical just feel some sort of sexual tension there
>feel guilty because im leading her on and also being unfaithful
>message girl and apologise for my actions and explain that whilst she is attractive and interesting (to soften the blow) i have a girlfriend and apologise for leading her on

i feel awful fellas, is the right thing to do to tell my gf? i wish i hadn't said the girl was attractive but it felt like i was being honest and it would make her feel better about being rejected.