I'm going to ignore my boyfriend
Why are you going to ignore him?
I'm very disappointed with him. He didn't want to hang out with me today but told me that he'll call me later on. After that I heard that he was at a party instead.
I understand you are upset about this. But instead of ignoring him, tell him that what he did made you upset. Communication is important.
I'm too angry with him to do that now.
You don't have to do it right now, but keep it in mind for soon in the future. It is important that the both of you are on the same page in the relationship to avoid further problems.