can someone give me relationship advice?

I’m back. For the last time hopefully. I met a girl who had a boyfriend. Should have stayed away from that one but the story goes on. Technically he wasn’t there for her. I wanted to be so I was. We got real close and eventually spilled our feelings out for eachother after kissing on the playground. Yeah cute huh? She told me things like “i would choose you over him if I had to”. The problem was, she “didn’t want to lose his friendship” so she never broke up with him. Another warning sign I should have paid attention to. Anyways, long story short she got a new job and became very busy. Suddenly she stopped talking to me and I got worried. My situation is quite unfortunate actually, I’m 17 going on 18. She was my first kiss. Not because I’m an extremely unattractive slob that can’t get girls, but because I waited 17 years for the most beautiful girl I felt happiest around. Sounds corny but you would have expected something else from an average teenage boy. Anyways after the lack of communication, I started texting her like a crazed psycho asking her for answers. She told me to give her space because her friends were leaving for college and she’s busy. I didn’t know how to handle that, my feelings were overwhelming and I kept bothering her. A month passes until one day she finally answers telling me that she “loves her boyfriend and she’s sorry she did that to me but sometimes Shitty things happen to nice people”. I really fucked this one up guys. I smothered her into not being interested anymore (at the moment). She really screwed me over but were young and dumb and I can admit it. I want to put all of this behind her and I. Her friends and boyfriend will be leaving for college in a month and I want to be there for her. Her feelings for me were real I feel like and I just pushed her away by being so annoying. We got along so well and it sucks that everything was timed so unfortunatley inconvenient, but I know we could mend this relationship. My problem is, I told her I would give her space but I want to let her know that I’m not a psychopathic texting maniac anymore and I realize the whole situation. Any advice in mending this relationship? How do I approach her. She’s an experienced (experienced with relqtionships)older girl and like I said i’m a rookie. Any advice would help and I appreciate you guys toughing out this long desperate novel. Thank you.