Lonely as hell here too at times. I'm feeling very sorry for myself atm because I don't know who to put as next of kin or emergency contact for me on form that I'm filling in! There. is. nobody.
DS stays with his dad (ExP), NP and DC's 2 nights a week. A house full of noise, laughter and chatter no doubt. When he's with me its just the two of us. I'm so hopeless at connecting with others that I've failed to arrange any playdates or make any friends for him (he's 3.4). DS says "I love being with you" which makes me blub, but I do ask myself if I'm enough for him and if he'd flourish more with his dad. 
I have no friends, no-one to phone or chat to, and can also do days when DS is not here, without speaking to anyone even on the phone. Nobody phones me, nobody has visited. But this only gets to me sometimes. Other times I'm foolishly optimistic.
I have joined a tennis club in the last couple of months though, as I used to love playing before toxic relationships clouded my reality. It's been a lifeline, honestly. So I'm counting myself lucky that I have that now.
If there is something that you love doing or used to enjoy, pick it up again and try to do it in a group, join something just to connect with others and have a life or interest of your own.
I'm in Greater London/Surrey if anyone in same boat would like to arrange meet up.
Chin up all! x