Juunen Ai - Decade of Love

From DP Scans and Fujoshi Bitches:

No matter how much he thinks about that guy, his best friend already has his lover by his side.
In high school Yuito couldn’t let go of the unrequited love he kept under wraps.
Nevertheless, ten years later is this a destined reunion with that best friend, Shougo? However, when he finds out that Yuito has a sex friend, Shougo is filled with rage!! Why does he get angry, even though he also had a lover...?

Then he comes to the bewildered Yuito to confess: “I’ve always loved you”?!