This isn't a marriage, the dynamic sounds more like an indulgent parent of a teenage girl. You need to stop beating around the bush with her and get serious if you want to see any changes, and don't expect it to be easy. More than likely she will get sulky, defiant, and disobedient, just like a teenager having her activities curtailed. I'd start off the conversation telling her this too. Does she work? If not, kill the cell phone you are paying for. She can call her friends when you are at work. When you are home, its husband and family time. Put your foot down on going to see friends 3x a week. Seriously!? She is a mother to two young children, why is she ditching her children to go play with friends half the week? Oh I agree, moms need girl time to get a break but this is far far above and beyond a break. I advocate a pretty hard line here, like once a week. And that's only if she has done her chores. Chores are spending quality time with you and cleaning. Not doing those? No play dates with other children!
Why do none of her friends come to visit her? I'll bet the real children are a hindrance to their partying. When she is out with her friends she can pretend she is single while 'dad' takes care of the house and babies.
Dood you sound like a really easy going, overly permissive husband. You need to dig deep and find your backbone. Without some hard lines, communications and yes rules she isn't going to magically change anything. More than likely her behavior will only get worse because she knows she can get away with it. Like a teenager she will continue to push those boundaries.
Tell her straight that your needs and the needs of the marriage aren't being met. Since she seems unwilling to make responsible changes on her own it will be done YOUR way until you see she can regulate her behavior.
What's the worst that could happen? She could run around with friends half the week going to bars and doing god know what, she could treat her family home like a hotel where someone else does all the cleaning, she could stop helping with raising and caring for her young children, she could emotionally abandon her tired husband....oh wait...
My point is, she is not likely to change unless forced to. If you change your behavior you have a good chance.