Wait, so you’re upset that he’s going out but he can’t stay with you anyway? So what do you want him to do, sit at home alone?

Depends on so many things.

How long have you two been together? If we’re talking a few weeks to a few months, I don’t think it’s surprising or bad that he’s got plans that are independent of you, it’s just unfortunate that it coincides with your dad being ill. If you’ve been together for years, I think that he should be more serious and considerate about you and your needs.

Did you ask him to be with you for NYE? If you did and he ignored your wishes without talking to you about it, that would be hurtful. If you didn’t bring it up, he might not have thought about it much and decided to do what he was always going to do, in fact he might even be thinking that you guys need family time and he doesn’t want to intrude. Especially, again, if this is a newer relationship.

When did he make these plans? If it has been planned for weeks in advance, it makes more sense that he’d carry on with his plans. If they were only made after your dad went into hospital, I might be a little hurt if he didn’t ask me first, but again that depends on the first two points I.e. how long you’ve been together and if you actually asked him to be with you on NYE.