My Childhood Friend.

Well, the Osananajimi tag is certainly in line with that title.
Hmm...So he points out that she has a boyfriend, but he seems pretty comfortable with just nonchalantly drinking with her and taking advantage of her while she's drunk.
Also, in that flashback..."It should have been me"? Yeah, you definitely should have done something a lot earlier. You fell behind, essentially, but it's not too late. I mean, if he made a heartfelt confession, she might break it off with her boyfriend for him.
...Although, I suppose he seems satisfied with their current relationship, so that's fine too. He has blackmail material too, after all.

"Nice guy" with no real spine.

Well, his personality sure seemed to do a 180 once she was drunk.

I laughed when he put his dick in her mouth like it was a bottle of water.

To Yuuto (In the words of a famous Merrie Melodies character): "YOU'RE DESPICABLE!" ... say-no-more, say-no-more.

Last page, prior plot for NTR. Run!!!