I think that people not speaking with you at events is very rude. I would be wanting to address this further. I think that Michelle's idea of getting to know his mother better is a good one.
There are a couple of other things you've mentioned which you may have to reconsider.
First is the distance thing: my hubby has family and friends who live an hour away and we rarely see them despite having all grown up together. They tend to organise events with others who are close to them. They'd see each other few times a month and we see them about once or twice a year if we're lucky. My sister and parents are 40mins away and live near each other....they see each other all the time - but see us much less. It's not about us, it's just the logistics. If you (or I) want to be more closely involved, moving closer to the friends and family is the best option.
The other thing is wanting your kids to grow up surrounded by cousins. While it would be nice to have, this isn't something you can plan for. What if you fall in love with a man who's an only child? Or a man who's siblings don't live near? Or a man who's sibling ends up infertile? Or even if he does have lots of family around, you may find people move away. Having cousins for your kids truly is out of your control - even if you keep working on the other issues, I strongly suggest you let this particular issue go.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.