Don't feel bad about the length bro! Long entries are the best to read!
It does sound like this girl may be a bit aloof. She never calls you? She never texts you? She only responds? Sounds like she wants someone to be around for now. Perhaps she's really not that into you.
The bit about her dating other men...That may be ok. I'm of the opinion that it's ok for a guy to take 3-4 different women or different dates one night of the week. Provided they are consent. This is not a permanent thing. This is a "I'm looking to find someone awesome now" thing. Think of dating as a way to find a best friend. You don't take one friend out at a time. When you look for a best friend, you meet lots of people. The more the better. This helps you narrow in on what you want. I think the same applies for dating. As long as she tells you that she's seeing other guys, and you're ok with it, then it's probably a good thing. It starts being a bad thing when she's steading seeing 8 different guys for 3+ months straight.
The question you need to answer is this: Is it worth being with someone when you are anxious that they will leave whenever? Is it worth being with someone that hasn't invited you to meet her family, friends or anyone? Is it worth being with someone who shows few signs of actually wanting to turn this relationship into something slightly more permanent? Is it worth your time and investment?
If it's not, go out and find someone else. Invest in yourself! Find some cool hobbies that you want to pursue. You'll find some other cool people to meet! I promise!