Guys, I caught my boyfriend staring at a girl's ass when she was jogging, it really hurt and I can't get it out of my head?

We have been together 9 years but it makes me think what else do I not know and I don't know whether to end the relationship as I am obsessing over it. I am that insecure sometimes I think shall I just stay single for the rest of my life.
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I need a bloke to say whether I am being stupid or not because I don't want to be with someone who looks at other girls or do all men do this to some degree? Would it not upset you if your girlfriend did it to you? Thank you cumere but he would just say that he didn't.
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Thank you all, feel loads better. I'm not a bunny boiler but I get that insecure sometimes it makes me feel ill and I thought that lads would give me a more blunt answer. Personally I only have eyes for my boyfriend but maybe I have looked without realising.
Guys, I caught my boyfriend staring at a girl's ass when she was jogging, it really hurt and I can't get it out of my head?
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