He already knew she was in love with a different guy AND he also knew that that same guy i...

idk.. he's just human. I think when reading g this you have to consider that they're still only high schoolers, and haven't developed mentally yet. they still have a lot of maturing to do, and cant be expected to be mature all the time.

Tell her broo Why is she being so harsh on him? He fell in love too She shouldn’t blame him when he wasn’t even trying to manipulate her ughh

When they did the game with the vote, he clearly voted 'no', so that she would think that ikkoku isn't in love with anyone. If you don't think that's manipulative, then I don't know what to tell you.

I know that they're high schoolers, but that still doesn't make it okay to attempt to manipulate with other's feelings. That's just how I feel. If someone did that to me when I was in high school, I would have been just as upset then and I would be now.

Bro listen when you truly love someone and have real feelings for them you’ll go through any path just to be with that person no matter how hard it is. That’s how love works. You can’t control the feelings you have for someone, so you don’t really have to blame him
And he already knew she was probably going to reject him because he knew she loved someone else, but he still insisted on confessing his feelings. It’s like he just wanted to get the weight off his chest at least. The answer he was gonna get was obvious anyway

Actually, I think that there's another possibility: He might have voted 'No' because he knows that she shouldn't be in love with her. So he'd denying himself. This would make more sense for his emotional frustration and the build up to him crying.