I'm going to continue using my ex's netflix and spotify
Why would you continue to use your ex's accounts?
Because no one will notice if I continue to use them
Even if your ex doesn't notice, you shouldn't use someone's accounts without their permission. It's against terms of service and doesn't allow them to consent to sharing with you. It could harm their account if it was discovered.
Why should I care about the account. He is not my  boyfriend anymore.
Maybe your boyfriend noticed it yet but he will eventually. So you will not be use it at some point of time. Why don't you ask your friends or family if they could share their accounts with you?