2 Books Found

Based on your description:

"Novel, read before 2023. Teen boy cares for his terminally ill mother and possibly a younger sibling. He attends a support group for teens with sick or dying family members. There he meets an older boy who rides a blue Vespa. They become close and may have an implied romantic relationship. Later the protagonist discovers the older boy's mother had already died and that he'd been lying to the group. Near the end, the protagonist is with his mother when she dies at home."