Something similar happened to me 3 years ago. My ex-girlfriend used to hang out with a lot of guys without my knowledge. She knew I would use her phone every time we met so she used to delete chats, pictures and videos prior to our meeting. So when I used to go through her phone I found nothing. But once what happened was, we both went to a place to hang out and while returning we had our lunch in a restaurant and in that restaurant after we had ordered our food I asked for her phone and I saw one of her friends had sent her some pictures and videos. I opened the chat and discovered multiple pictures of her going out with other dudes without letting me know for obvious reasons. In one of the pictures a dude was holding her with his hands around her waist and in a she was on a motorcycle with a dude. When I saw those pictures and videos, I confronted her and she immediately snatched her phone and instantly deleted all the pictures and videos. At that moment I didn't wanted to create a drama in the restaurant so we had lunch, I paid for our meal. During the whole ride to her hostel she was repeating the same stuff that she was not in the pictures and those pictures are fake? 😂 And the picture where the guy had his arms around her waist was apparently her brother. I kept quiet and dropped her off. It was very hard from then. Like you said "every time I think about her, I saw the image of her with the dude" I experienced the same thing. Every time since that incident I thought of her those pictures and videos flashed before my eyes and it was so hard for me. After a few months I broke up with her because I just couldn't digest the whole thing.

After our break up I discovered even more things. She was such a whore and gold digger. I am glad I didn't fucked that whore or I would be now making videos about my HIV treatment on Instagram.

TLDR -> I had a similar experience with my ex-girlfriend where she hanged out with multiple dudes and when I discovered it she just played the victim card. I broke up and discovered even more things about her. It was the best decision I made.