Final answer:
Zhang does not have to continue with sexual relations if he does not want to, as ongoing consent is required in any sexual activity. Prior involvement does not imply future consent.
Step-by-step explanation:
No, Zhang does not have to participate in sexual relations if he does not want to. Consent is a crucial aspect of any sexual relationship. Prior sexual activity between Jessica and Zhang does not imply future consent, and Zhang has the right to refuse to continue sexual activities at any time. It is important for all individuals to respect each other's boundaries and decisions regarding their bodies and relations.