With some guys it's easy to know when they will ask you to be their girlfriend, but with some guys it's not as easy. Most men hide their feelings very well. Sometimes if a guy starts to call you a lot, seems to want to spend a lot of time with you, and asks personal questions, then he may be thinking of asking you to be more than just a friend. Some will just observe until they feel it's the right time.
You should feel the chemistry. Watch his behavior. Does he treat you the same way he treat his friends? Don't know? Meet his friends. When you with him be positive, don't push yourself onto him, but the most important thing is to be yourself. Some guys will lead you on because they like to receive attention from different women. The only way to find out if he wants more from you is to pull away and watch. Wear clothes that makes you feel good about yourself, clothes that makes you feel confident, something that he would be attracted to, something that shows off the best part of your body. If you have nice legs wear shorts, nice chest - go with a dcollet... If he is not going after you and you feel like he is the guy you want - there is nothing wrong with flirting or giving him a hint. Grab a case of beer and ask him to watch a game with you (his favorite sport) - just you two. If he comes by himself you have a chance. Work the situation, make something to eat (if you know you're not good at cooking order pizza or his favorite food), crack some jokes during the game, let him relax, than if the game is not tense or there is a commercial ask his opinion on something, look into his eyes while listening to his answer. Your eye contact will give him the message. Dont look tense, look relaxed and almost (!) smile.
If he brings a friend with him - he is trying to tell you he is not comfortable being alone with you.
2.If you have been sleeping together but haven't had a conversation about being girlfriend and boyfriend (being exclusive): That's a tough one. Technically you already agreed to give up the goodies. It's hard to capture his attention after you got physical. But you can always try. If he enjoys your company and you have a lot in common, you have a shot. He will come to you and you will see him reaching out to you more, coming to see you when you didn't plan a date, sending you little gifts.
You can't make him if he is not ready to be in a relationship with you. At that point you should let go if you don't want to get destroyed by this disappointment - the sooner the better.