With friends he tends to be a little wary of the new person if it’s a stranger that his friend has picked for a romantic partner, rather than being a friend to them prior to romantic whatever. He’ll be a little protective initially, but he’ll chill out when he sees that his friend is at ease and safe around them, or he sees that the partner in question seems alright.
Now if he somehow got himself mixed up with romantic feelings for someone and they fell for someone else?
Honestly, he would be a mess. As mentioned in a previous ask, he’s very stubborn about saying how he feels due to fears of rejection or ridicule (bc oh no, emotional vulnerability!). So right off the bat he’s in a bad place, because how the hell could he ever open his mouth and say how he feels when they’ve already fallen for someone else? He’d just be in the way then. He doesn’t want to ruin the nice thing they have going for them, they have someone that makes them happy, he should be happy for friend!
Which…he’ll try to be. At first. But the longer it goes on, the more it hurts him, the more he gets quieter and more withdrawn and upset until the point that he might start avoiding them altogether. Much sads, much booze, much isolating himself by wandering off in the wilderness for days at a time. The friendship would likely deteriorate into nothing without intervention or forced circumstances, by which point J’hasi would likely leave the area entirely and not come back.
So in a way, I’m kinda glad that he’s not really inclined towards such things o_o;;;