It's called pride. You don't want to be loved out of pity and you need to be sure that it isn't. Falling in love isn't supposed to be that easy, especially when you kept yourself loving that person for so long, the uke, Ichika, didn't have to love him that long but he did, so reciprocating it should be properly thought through.
Well I mean he says he loves him but imagine 10 years of secretly giving off hints (in the ukes case probably subconsciously) that went unnoticed. Now that you think oh maybe he likes you but maybe he's just confused after all he did just break up with his girlfriend. Maybe he's just so desperate not to lose you as a friend that he's saying this. I'd be really cautious too tbh

Cute I like it. The stort is so sweet, and I like best friend to be boyfriend story. But if can complain a bit the uke is too tsundere after the seme accepted his love. Imagining the guy that you loved for 10 years without hope and you already giving up, but in the end he accepted your love. I expected more of happy expression.