Any writing questions can go in writing/novels I think, even if it's writing for a comic.
Here's the thing. For real people, you may not need your reasons to be super clear because it's your life. However, with a story, you want it to make sense to the audience, so it's definitely important to know your character's motivations. They might be shallow, they might not be, and not everyone is super deep. But if they have a really strong attachment rather than just physical attraction to the person then there will probably be a deeper, more ingrained emotional reason.
I don't know your characters, so I can only give info based on what I know, and what I've written, but if your leads have any past traumas that their crushes counteract that can definitely be a big reason that they like and are so attached to their crushes.
Example: My leads Kattar and Alicia have been friends since Junior have had crushes on each other for quite some time. Beyond the fact that they both just find each other attractive in general, they are really attached to each other as friends as well. They both ALSO have some pretty traumatic past experiences, which leaves gaps the other fills.
Alicia: had a pretty jerk boyfriend who never spoke to her kindly and didn't really respect boundaries, he would grab her and move her forcibly like she was a doll rather than a person. Her crush Kattar never EVER touches her without permission, speaks to her kindly, and is defensive of her when other people treat her with anything other than respect and gentleness. She also grew up with pretty inconsistent and unreliable, negligent parents, and Kattar is a very reliable person you can count on to do what he says he's going to do, and tries every hard to take care of her, even though it's not even his 'duty' to do so. She's also been very depressed and lonely for a long time, and he tries very hard to make her happy. So you can see her reasons there.
Kattar: Has the trauma of never having met or even seen a picture of his father once in his life, and his mother is all about being 'rational,' 'organized' and 'having your life under control.' She also complains a lot about other people, which causes Kattar to worry about living up to her expectations. Alicia doesn't try to hide her emotions most of the time, and she doesn't consider feelings, and expressing positive emotions about people stupid. She tells him how she's feeling when she's having a bad day, and though he basically never tells her, asks how he's feeling as well. She doesn't trash people, but rather, always tries to find the good in people and give them the benefit of the doubt, even when they're being a real jerk to her. She tries to see people's emotions and motivations behind their negative behaviors and love them through it, while Kattar's mother's MO is to try to distance herself from people whenever they do things or behave in a way she dislikes. On top of that, she's a very intuitive person, who asks questions so that she knows what people like and dislike, and cares about and shows interest in their interests, or at least is willing to engage in their hobbies with them, regardless of whether she finds them interesting or not, which definitely helps him to feel less isolated, considering the fact that his mother has a tendency to assume what he wants or needs rather than asking.
On a maybe slightly insecurity-based note, she also allows him to feel useful and needed, at least before the accident that paralyzed him, so it helped him to counteract the trauma he has from his other always complaining (albeit, she never means it as an attack towards Kattar, but he hears it all the same) that 'men are useless.'
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So I hope that looking at it this way helps you to be able to figure out how to pick out and find the reasons and motivations your characters have for liking each other romantically, or for liking anyone for that matter. Again, it, doesn't always have to be super deep, but depending on the level of attachment you intend for them to have to each other, the deeper the attachment, the deeper the reason should probably be.
