So, a couple of months ago I got into a new job where I met this guy I few years younger than me but we felt a really good connection as friends, even siblings, our stories are very similar and we both have suffered a lot, the difference is that since I'm older I have most of my problems solved and he doesn't, he is still in a bad shape with regular problems like every day, and because of that he just decided to break up with his girlfriend because he didn't felt loved anymore and he felt like he was a burden for her. They were apart for a month, and during that time I worried a lot for him so we started to hang out a couple of times outside work, was during that period that someone told his ex that he broke up with her because he was cheating on her with me, and that he was still with me. Eventually they got back together, he explained that the cheating thing was a lie and neither of us is interested in that, on the contrary (I rather the female company) so they are good. He talks about her like he is super in love, he even sees himself married with her in the future, but the thing is that tonight I was scrolling through tinder and I saw his girlfriend profile, it's her I checked everything and I'm sure it's her, but I don't know if I should tell him or not. I feel like if I do I would be stepping on a problem that's not mine, and if they do break up I don't want her looking for me to fight for ruining her relationship (she's that kind of girl), but at the same time I feel like if I was in a relationship with someone I would like that my friends tell me if they are cheating on me, like I wouldn't like if they kept it a secret.