It's set in high school or uni and has one guy being really cute and popular and 'stealing' the girlfriend/s of the other (I think she turns out to be a lesbian). The not-popular guy spends the whole manga jerking off, there's an end panel where a rabbit (?) jokes about it! Popular guy walks in on him at some point. During the first 'love scene' they are watching a DVD in popular guy's room or dorm. I think popular guy at some point tells not-popular that he thinks about him when he masturbates as well.

Is it Miteranneeyo?

That's it! Thank you so so much 😀 xx