Again, I think you are framing this in a way that isn't helpful to you, your marriage, or your wider relationships.
The way that we feel about things is something we can control and alter. You can choose to see this as you being a martyr and 'sucking it up' in suffering silence (and you're right that, far from being self-sacrificing, this is likely to make everyone around you completely miserable), or you can see it as putting on your big girl pants and not sweating being apart from your husband for a couple of hours while a ceremony takes place, then turning up with a big smile on your face to celebrate with the happy couple in the evening.
It's OK to have feelings of sadness about being 'excluded' - but it's also important to realise that it's not all about you, and that there is a dynamic here between your husband and his ex-wife that the children are trying to manage in their own way.
You don't have to get along like a house on fire with your DH's grown-up children, but you definitely don't need to create a rift by demanding that he chooses between them and you, and sulking if he refuses to do so. Most relationships in life, with family, friends, partners aren't on/off but are created every single day by a constant process of communication and negotiation, in which compromise is an almost constant state. You are unlikely to find anyone as a partner who doesn't have some other ties that will have to be balanced with love and care for you. That's how life works. If you have feelings of abandonment, disloyalty and upset at normal adult compromises, then there may be some deep-seated issues there that need addressing, possibly with a counsellor?