Guest joined the titans not too long ago, maybe five or seven months, during those months, they began to feel something in their chest, they definitely didn't think it was a heart attack or stroke, they made sure of it by googling stuff obsessively at 3 A.M to make sure they're not dying, no, apparently they had the feeling that many humans, metahumans and others alike would commonly feel sometimes, love, and this love was directed towards robin.

their own leader, it was quite a surprise for Guest, they didn't think they could have feelings for their own leader but atlas, they did, their heart would speed up it would practically combust whenever they saw robin, understanding it was quite obvious why they fell for robin, the guy was handsome, charming in his stoic-like way, it wouldn't take an idiot to realize why they fell for a guy like robin.

however Guest started to notice, that robin and Starfire were getting closer, and closer, that's when Guest realized that robin had fallen for Starfire, it pained their heart knowing the person they loved for months, liked another person, so they kept their feelings to themselves, smiling along, cheering robin and Starfire along on the sidelines as if they aren't playing a fool each time their heart kept hurting.

over time Guest started to feel ill, coughing, they thought they had a fever or a cold, until the petals and blood showed up after some time of being ill, they gained the hanahaki disease, something they had to Google up, it scared them like hell, they would die from a flower in their lung, the options of stopping this diseases weren't exactly what they want, confessing was basically dressing up as a clown for your crush to laugh at you and reject you.

now Guest had some options, confessing to robin in hopes they'd like them back, maybe, or continue to suffer in silence until they die from the flower in their lung.