I still don't understand how Jere could choose to be with Belly at the end of season 2

In Jeremiah's own words, he only liked Belly at the end of season 2. However, he knows that Conrad is still in love with Belly and that Conrad and Belly have only been broken up for six weeks after being in a serious, committed relationship for seven months. Conrad told him twice that he is in love with Belly, including when Jere forces him to admit it at the motel, but then Jere still chooses to get with Belly anyway. How can he do that to his brother? He knows that Conrad and he are also still grieving the very recent death of their mother, so again, how can Jeremiah do that to his brother? How can he add to his brother's pain like that? He also saw how devastated Conrad was when he caught Jere and Belly making out on his car. I don't understand how Jere can do that to his brother, and I don't know how the brothers can come back from that.