So for context I'm 17 F and my friend (let's call her Mia) has been my friend since tenth grade. We're not super close she's more of a school friend. Two days ago I saw her boyfriend (let's call him Mike) I met him last year and I didn't think anything of him. He was cool but I'd never make advances on him (Bc I'm a lesbian and no one at my school really knows except for two people that aren't them) So yesterday I saw Mike in the hallway outside of his classroom. There was another girl who was playfully slapping his cheek and touching his face in a non-platonic way. I wanted to get a picture but never got the chance as the hallway was packed. Over the night I thought about what I seen. I had a bad feeling about it so this morning when I saw Mia I stopped her and asked her if Mike and her were still together. When she told me yes I told her what I seen. I told her that it could be his cousin or something (which I doubt) I asked her if she wanted me to get hard core proof since it would only be my work against his and she said yes. I told her that I didn't want them to break up over something that was blown out of proportion and to not make a move or tell him anything until I delivered evidence. Today I seen him and it seemed like he was looking for someone. Idk if it was me or not. Now I'm a little worried if I can't deliver proof? If something like this were to happen to me I would want my friends to tell me right away but now I don't want Mia to think I'm trying to break them up on purpose or that I want her boyfriend. Was I in the wrong for telling Mia?

Edit: when I say a non-platonic way I mean caressing his cheek, grabbing his chin, ect.