single mum, help with ex

I have currently found myself being a single mum to my four year old son. My partner/ex says that he doesn't like it that I can't except that he still wants a very close relationship with his ex wife - mother of his two other children,he still wants to go out for dinner with them and be round her house for the night, days out and go away.

I can't except this. Im happy for him to see his kids obviously but why his ex wife? Am I wrong? And because of this he wants to end it. He still wants to have a relationship with me as in occasional sex, stay the night and see his son when it's convenient with him and when he's not out or sleeping with someone else.. I just have no idea what to do and feel so lonely. I know people will say stay away from him but I have no friends since having my son, I can't speak to my mum about this and all my sons friends mums are married. I have tried toddler groups but they are very clicky.

I know it sounds stupid but I am scared of being alone without someone to share things with and have the night with or go out with. When my son is in bed it's very lonely and I get fed up always going everywhere on my own with my son. He sees his other children lots and every school holiday but I am just ileft to look after my son on my own. He doesn't even pay me regular money 

Any advice?!

Tags: visiting dad mum