quite the opposite actually, jaehyuk takes the girl to talk to prevent anything bad happening. garam hears jaehyuk and the girl talk and the girl says to jaehyuk at one point “are u playing with him, are u gonna get rid of him now that u could have him” something along the lines. and after jaehyuk tells the girl off, he goes back to see garam standing behind the door and realize he heard everything. then he thinks he will misunderstand and gets nervous, trying to clear any misunderstandings garam could have. BUUUT, even to jaehyuks surprise, garam actually shakes it off, saying it’s fine and that jaehyuk did/say nothing wrong. then they take off to see the movie garam planned for them to see. SO, SWEETIE, NO. GARAM DOES NOT ACT AS IF HE WANTS TO SABOTAGE THEIR RELATIONSHIP, IN FACT, NOW, HE TRIES HIS BEST TO MAKE IT WORK.
Nothing here is Garam's fault. Garam wasn't angry and didn't make a big deal of Jaehyuk's talk with Shinjoo because Jaehyuk didn't do anything wrong. He already told Jaehyuk that it was fine, Jaehyuk just didn't buy it. Garam continued the date as usual but Jaehyuk couldn't move on until he brings it up again at the river where Garam reassured him and confessed that he likes Jaehyuk more than what Jaehyuk thinks.
after reading the raws garam acts as if he WANTS to sabotage their relationship