Dearheart, you're not a failure as a MOM!

And I know what loneliness is, but things change. Nothing ever stays the same.
You say your family doesn't understand -- but have you explained to them how you feel? I mean, how you REALLY feel? Do they know what's in your heart?
People may SEEM not to care but it's because they don't REALLY understand, my friend.

And that's because we figure they SHOULD understand. We assume that they SHOULD know. How should they know if we don't tell them? They aren't mind readers. I've assumed this myself. lol I figured my family should know too -- until I got to thinking about it.
They can't know unless I tell them exactly HOW I feel and why. I can't blame them because it's no ones fault. It's not even mine. Depression is an illness. Yes, depression. When you're lonely, you become depressed and that's hard to deal with by yourself.
Talk to your doctor. He can refer you to a good therapist. Therapy is a wonderful source of help and you'd be surprised at how much it helps -- not just with loneliness but with other issues that you don't even know you have. Loneliness most often stems from other issues -- the therapist can help you "find" those issues.
I wish you the very best, my friend. God bless you and please take care of YOU. Hugs, Lee