Alec had no place to make a remark about sex without love. Technically he had done that whole sex without love thing as well, but that was kind of what had lead to the relationship even starting. Not that he was going to tell Jace that. They were in a relationship, but he didn't have to share all the details of his love life with Jace about Mark.
So instead of saying anything he just made a face that showed just how much he disapproved of the arrangement his parabatai had with Damien.
"I don't want this relationship to stop either, Jace." He could see the hurt and emotion on his brother's face. Alec could tell that any wall that Jace had crafted was now gone, everything was out in the open at the moment. Hell, the fact he apologized was proof of that. "Look...I am not going to just end our relationship because you made a mistake. I decided to talk, remember? Jace, your my parabatai, my brother, I wouldn't do that to you ever. I just-"
He didn't want Jace sleeping with anyone else. It wasn't fair to Mark, it wasn't fair to Alec. He spread his hands wide helplessly as words started to fail him.