Most guys miss the signs. Women think they are being obvious so when a guy doesn't follow through they interpret it as lack of confidence or disinterest. There are plenty of good resources out there on body language. It is a confusing language as women express interest differently and you can get some false negatives especially with shy girls and you need to be able to evaluate the big picture and look for clusters of signs. In your post though you picked up a few already i.e. proximity, finding excuses to talk to you.....if you pay attention you'll also probably see they treat you differently from the other guys in the group.
Dating apps might work better for you. If these girls are developing crushes on you while you barely notice them it probably means you are very good looking. On a dating app it is a lot easier because if they like you they swipe right on you and reply to your messages and agree to exchange numbers and go on dates.
Once you are over that hurdle I'd agree with the poster above that missing cues is far more of an issue in getting laid. For hooking up it is a case of you have to strike while the iron is hot and there is a narrow window of opportunity and they will judge you more harshly if you fail to to lead. For relationships it is more about the connection so if she is enjoying your company she will be more tolerant if you move slowly. Even then there is a limit however and the third date rule is a good rule of thumb.