I need help getting and maintaining a relationship B/c I'm tired of failing over and over again

(I am 17) by a very loose definition of the word relationship I have had 8 relationships and they all eather were going to turn Into a relationship or they ended withing 2 days except 1 that lasted 2 months but that was b/c I didnt see her for 7 weeks and I prefer to end them in person b/c it's a lot easier to take for me but this last one that I truly liked and when I was with her for that few days I felt happier than I have ever then ... Day after new years She started being dodgie saying she was to bizzy to hang out today then tommarrow then next week then well you get it and I have seen this part of a relationship well my relationships many times before and I'm just really tired of always feeling like a failure and feeling alone. When I'm with someone though I be myself so don't give me that bs I wouldn't want to be in a relationship as someone else but myself is just not interesting and I just don't know what to do I was raised to be a nice guy and I used my manners but he'll those don't get you anywhere the nice guy seems to never get the girl it's always the crazy maverick kind of people I see In relationships. I know I kinda just went off on a rant a bit but I could use some really help not like a be your self and use your manners kind of stuff that hasent help me yet and I seem to keep doing something rong so please if you can I need help

First off, nice guys are the BEST ever, so don't stop being a nice guy because you're meeting girls who don't appreciate that.

Is there a "type" of girl you fall for? Is there a pattern to the relationships, besides duration?

There's a big difference between being a "nice guy" and being fun to be with. Consider the questions below. It might be worthwhile to ask what your close friends or family members to rate you anonymously. Make up a multimple choice questionaire so they just check the answers.

Do you smile a lot?
Do you have a happy, positive attitude?
Are you funny?
Do you have self confidence?
Do others respect your opinions?
...
You can probably think of some more specific questions to add. The point is we don't always look the same to others as we view ourselves. Any way you can get a realistic idea of how you appear to others will help answer your question.