I imagine widowed and divorced of both genders feel this too.
I wouldn't say that I'm a 2nd class citizen in my parish - they truly are incredibly supportive. However, in many ways it's that I straddle so many groups; people aren't sure where to put me. I'm a widow, but I'm under 40 (one of 2 in the entire parish to the best of my knowledge). I have a child, so I don't exactly match the typical profile of the under 40 young adult Catholic. My child is in the parochial school, but we're certainly not the typical school family either. Frankly, my parish does recognize they haven't done a great job with single Catholics (younger and older) and recently I've seen some signs of change, but still nothing that speaks to me. I'm the type that would volunteer to make the change I want to see, but I'm a full-time student and mom, so it's just not possible right now.
Other parishes in my area do have more active young adult groups and/or widow groups, but not being a member of the parish, it's hard to keep up with their activities. I also do think a parish my size (5000 families) can and should encourage greater involvement.