It is possible they can sue you for the rent due from end April to August. If the agreement(s) between you and your roommates were purely oral (sometimes called verbal), then you would be a month-to-month subtenant of the two tenants on the lease; in that case, you would only owe 30 days notice (or rent).However, you state there are "text messages." A written lease does not need to be a single document titled "lease"--depending on exactly what the messages said, it is possible that those messages (one or more of them, or all of them in the aggregate) could possibly be held to form a written sublease agreement between you and the tenants. It's not a given they'd win if they sue you, but from what you write, it might be possible.