@2025meme, I agree with everything @PyongyangKipperbang has said.
Of course you are sad that you won’t see your H on his birthday. In addition, your gift to him has taken a different turn that makes you uncomfortable, and that is valid.
(1) You hardly ever see this man. You cannot go to the festival, but you hoped he’d have a good time with his mate and his gf. Now, as PK pointed out, the outing has turned into a party, which will undoubtedly change the whole dynamic. The celebration will now include several women who are not long-time friends of H or of you as a couple. This has unsettled you because …
(2) Your H cheated 3 years ago and you do not trust him. He shifted the blame for his faithless behavior to ‘believing you were cheating’, which was ludicrous. With his history, I understand why you feel uneasy about this upcoming event which has turned into a party group with new women, as he has previously trashed his fidelity.
@2025meme, may I ask why you have stayed with this man who abused you via his adultery and then refused to take responsibility? If he has not shown remorse by making amends, strengthening his boundaries, and investing his emotional energy, time and attention in you and your marriage, then why are you sabotaging your peace of mind by staying?
Are you going to speak to him about your discomfort regarding the festival?