Hi all have namechanged as have a few rl friends on here who know my normal name.
I am having trouble being a good friend at the moment and wonder if I am just a nasty bitch or if others would feel the same.
Have been friends with this person since high school (about 14 years) and we have gone through stages of being very close and then hardly seeing eachother due to relocation etc, we have been back in close contact now for nearly 2 years and speak regularly on facebook and see eachother once a week.
I have a 5 year old and 2 year old twins and she has a 3 year old son who has a genetic disorder which means he is unable to talk and can only do limited crawling and a small amount of weight bearing and is currently pregnant with number 2 (no way of knowing if they have the same problem until born and had a blood test)
I have been finding the last few months very difficult with meeting up every week and have been cancelling quite a few meet ups 
I think its because as my twins get older and more independant that her DS's problems have become more apparent and I am finding it very limiting with what we can do together.
If we go to a soft play my two are off and into everything whereas her DS just sits and wants her constant attention which means I either limit my two to staying put or chase after them and let them have fun meaning we have no time to chat!
We tried going to the local park with a picnic in the school holidays with my 3 and the both of them but ended up leaving after 10 mins as the twins had learnt how to open the gate and escape and trying to stop them and keep an eye on my eldest was just way too stressful for me, my friend couldnt understand why I wanted to leave and kept trying to get my to go to another park which is just as bad but by a river so even more stressful for me!
The only real option is for her to come here (I dont drive) which is fine as the twins and her ds play nicely except she will turn up at 930am and doesnt leave till at least 230pm and thats only because I am off on the school run and if she doesnt have to pick her DH up from work she will come on the school run with me and stay till about 4pm.
This means I end up having to do lunch for us all or go hungry and as I tend to have leftovers for lunch it means me having to buy extra food in especially. It also means that I dont manage to achieve anything when she is here and the house is like a bombsite when she leaves!
The other problem is that all she really does when she is here is moan about how shit things are for her and how shit the council/HA/NHS/HV etc is and then if I mention I plan to do something she tries to get invited, I kinda feel like she is trying to take over my life!
She does have other friends she sees and does attend a toddler group with her DS so its not like Im the only person she sees each week.
She is being made redundant next month which means she has even more spare time and is pushing for me to help her fill it and I feel like I really dont want to even meet up once a week let alone more 
Am I being a complete bitch for wanting to withdraw from her? and should I be making more allowances for her situation or should I accept that the friendship has started breaking away again?
Also how do I explain to her how I feel without sounding like a heartless cow? or maybe thats exactly what I am 
Any advice gratefully recieved TIA