<human>: Can you condense the text into three sentences or less?

I have been into relationships... and I never had a problem... I have had all situations of break ups, cheating, insecurities... and everything and handled it always well... I even give advises on subs about relationships and everything... but i guess everyone has his time to need help not just give..
This kind of back fires at me... since now i am in a long distance relationship with an amazing girl (24) and i trust her with everything... 
we talk all the time and we send pictures and videos and its just perfect... and its healthy too cuz we have our arguments and we make up... so everything is normal... 
but when I see how couples cheat ... and friends cheating with others and everything... it just plays with my mind... thinking she could never do that... but what if she has just a moment... what if... and those situations start building up in my mind and i cant help it...
i know its not healthy and for it to work i need the trust and give her a break... and i do... i do trust her... but u never know the situations... and how many couples were so blindly trusting of each other to one day something happens and they never see it coming...
I just want to know what can i do for these things that keep popping up and making my mind go to situations that are not right to even think about... what should i do ?
<bot>: currently in a perfect long distance relationship but sometimes doubts and insecurities come from looking around me at failures, what should i do to remove those doubts?