When do women just start being straight with you if they aren't interested?

I am 18 so I know I am young and maybe I will learn a bit more about what is going on in other people's heads with age and experience. I also understand that there is far more to life than relationships. I also have no anger towards women for not being interested in me, but I do feel quite a bit of regret about the time I have wasted talking to girls that simply aren't interested in me. I understand "Taking a hint", but I always just end up being pocketed by girls for various reasons. I have been used before by a girl to make her ex jealous, lead on twice (And by that I mean actually lead on.... Not just the inability to take a hint.), and have been the subject of jokes for putting myself out there by the friends of girls who I have talked to.

As I said before, I understand how to take a hint. Usually if I hear, "I have plans" twice from a girl after asking her if she wants to hang out I just kind of stop trying, but hearing something like, "I definitely would, but I have X going on..." Implies to me that she is interested. I always feel like girls do this as a way of putting off making a decision about whether to go do something with me or not, like if they have multiple guys into them or something and they want more time to choose. I have multiple girls talking to me as well, but I really don't want to hurt any feelings going out with one after another had just turned me down but said they want to hang out.

Its not like I am horrifically ugly or anything, I am roughly about a 6-7/10. I can be a bit of a jackass at times, and that's a part of my personality that I can really understand if someone wouldn't want to deal with in a relationship. I just feel a sense of frustration with my lack of ability to understand what is going on in other people's heads sometimes. I mean its not like I possibly can know who else they are talking to, or why exactly they might say that they would like to go do something when they don't. I don't know, I just really wish that people would be more upfront with their emotions.

Do women ever get more upfront and honest with people? I guess sometimes it's up to me to straight up ask if they have any interest in hanging out with me, but that can be an extremely awkward conversation that I generally try to avoid.