Some people are beong a little disengenuous, and rather unsupportive 
There's a huge difference between being alone and feeling lonely. The loneliest I have ever felt was in a room full of people I knew very well.
And yes, children are fantastic, but they also mean that, however low you feel, you cannot 'run away' (even emotionally), or even get out of your house for 5 minutes to escape the loneliness. They also restrict your opportunities to go out and meet other people and do things that make you feel good about yourself.
It's hardly all good.
Childen also tend to take a lot more than they give and rarely, if ever, make an effort to meet your needs, which is how it should be, of course.
poison it won't always feel like this.
Do you want to talk about it a bit more?