This is actually a fairly common issue for men and women who enter second marriages or deeply committed relationships following divorce. In your case, it appears that you and your partner have two significant differences in your family situations: First, he has family nearby and yours is far away: and second, he has grandchildren and you have independent adult children but do not have grandchildren. Naturally, both of these factors tip the scale toward your partner having both more desire and more opportunity to get together with his family and it sounds like his desire to do so is very strong.
I can understand his strong desire to have you involved with his family. I’m sure he sees you as a very important person in his life and it feels natural to him to include you in his activities with his family. I’m guessing he would really like his family to get to know you and care about you and to see you as a part of their larger family. Integrating a new spouse or partner into a pre-existing family culture can cause shifts in family dynamics that can be tricky after a divorce.
For your part, although I don’t know your own history of relating to your extended family, it is often true that we find more enjoyment and meaning in relating to our own relatives than to someone else’s relations. Certainly, many adults find it challenging to integrate into their partner’s family and new partners frequently encounter reluctance, resistance and even occasional hostility from some members of the family along the way. It sounds like you want to be connected to his family, but not necessarily to spend the same amount of time with them that he wants to spend.
While your partner may desire you to be a part of everything he does with his family, it will be important for you to negotiate some limits with him about how much time you want to spend and what kinds of events you wish to participate or not participate in with them. These decisions will influenced by the quality of his own relationships with his adult children and grandchildren and what he sees as the more and less important events or types of activities he really wants you to share with him and his family together.
For example, birthday celebrations, anniversaries and holidays might be three types of events when your presence would be most desired and appreciated by both your partner and members of his family, while casual get-togethers might be viewed as less important for you to attend. You may choose to attend or not to attend these kind of events and reach the understanding that this is not a negative reflection on either him or his adult children.
There are no pre-determined norms for this sort of situation. Although couples who are married may feel more internal pressure to have their new partner at every family event, this is really up to the two of you to decide. The family will take the lead from your partner. If he presents this as normal and not intended as a slight to the family, they will usually feel the same and if he conveys resentment about your absence, they may wonder about your relationship.
The greatest challenges will be your ability to stay honest with him in the face of his disappointment and his ability to accept that you are both part of his family, yet not attached to them in the same way he is attached to them. It sounds like you have a healthy enough relationship to be able to negotiate these understandings with one another. There are many ways of relating to a new partner’s family and usually plenty of common ground for working out these types of differences in relationships.