need help because im afraid i might have cheated or disrespected my gf

Hey guys so before i start i need to explain something, im (25 Male Bissexual), and im dating my gf (25 female bissexual) for about 6 years now.

So let me explain something about 1 and a half years ago i recieved a dick pick as a joke from a friend ( he doesnt know im bi only my gf knows), and i told him that shit is gross as fuck and that the next time he sends something like that im going to put it on the internet (as a joke i wouldn really do that), he didnt send anymore photos like that. A few months after that i was masturbating, and i remembered that pic and got curious and tried searching for it but didnt find it, i masturbated normally, but after masturbating i got this post nut clarity, and got really grossed out because of the idea of me searching for my friend dick pick and triyng to masturbate to it, a few days passed and i tought to myself, did i cheat? Since that it comes and goes but i feel SOO guilty over that that sometimes i cant stop thinking about that thinking to myself that what i did was wrong and feel so mad at myself, thinking that if my gf did the same thing i would be sad. I really need help clearing my head, what do you guys think, should i just move on? am i thinking to much? I try so hard being a good boyfriend but thinking about that breaks my heart thinking that what i did was really bad, Please help..