Being a stay at home parent can be lonely..

Why do I feel guilty when I say that? I have two beautiful kids who are my whole world and an amazingly loving husband who is my best friend. My days are filled with constant play time, laughter and love. But some days I do feel lonely in this life as a mom, I devote %100 of myself to my family and in that I have lost a lot of "friends" or people I associated myself with. Most for the better, leading two completely different lives with most of the "friends" my age. Still i sometimes catch myself wishing for a friend or two, people who had common interests who I could chat with and make play dates or ladies night out plans with. Why as adults does it seem so much harder to make real friends? In school I was a social butterfly and had tons of "friends". Don't get me wrong I try to meet people, I take the kids to the park and try to socialize with other mothers. It usually doesn't go any further then small talk and moving on to another side of the park chasing after your kids. Iv taken the kids to the library for story time and play groups, and most moms are in cliques and not very sociable with outsiders. So here I am questioning why I don't have real friends, why I even want them, why my life isn't good enough just my little family. Am I wrong for feeling a bit lonely? Am I wrong for wanting to meet a new friend, hoping to hit it off and have our kids be best friends?! Maybe..