I feel like Shiro will have a crush on Matt since he's grown and matured since he last saw him.
I feel like if Shiro ever liked Matt, he would have liked him before and after they found each other. Maybe Shiro would have never thought about it, maybe it would have just been a nagging thought at the back of his mind, but Shiro would have always thought Matt had something that made Shiro act a little differently with him than anyone else.
And if he hadn’t realised back in the Garrison days that he liked Matt, I think just the relief of knowing Matt was alive thank god would be enough to for Shiro to realise that he likes Matt. More than jus friends. More than he realised. More than he ever thought he would? How does he look either Pidge or Matt in the eyes now, oh my god