In search of adice and help. I so want her back but fear its too late

I will try to give a decent overview of the situation. It feels as though thr early stages of our relationship don’t matter now and i’ve been too emotional and have been ruining it for months. She was on old friend who had a soft spot for me. She lived about 2.5 hours away by car so was a long distance relationship. She was living with someone she had been with for 5 years living together for 2 but was very unhappy with the relationship and growing resentful of him. Over the course of at least a year we started speaking online all the time until it got to the point that we wanted a relationship, we loved each other and she finished with her boyfriend and started seeing me. Over the course of another year we were seeing each other regularly a lot of weekends and alot of time in the school holidays too as she is a teacher. During most of that time it was magical and I know she would say the same. We had a real connection we laughed together lots, never for a second got bored of each other and the sex was amazing. She regularly told me it was by far the best shes ever had and never thought it could be so good. It was the most real relationship either of us had ever had. I had no job and not much employment prospects and she wanted to change me and I started doing a course that meant i could apply for university and this was going well for a while. In the last few months i really blew it. I started smoking weed and got into a depressive repetitive cycle, I went back to how i used to be before her and went back to having no motivation and was saying i wasn’t bothered about this course anymore. Anyway she would say for the last few months I was rejecting her and lying to her and that i had mood swings. I blew hot and cold on her and i regret it so much. I was stoned and not thinking straight. (btw please dont say i need drug counseling i am determined to fix myself now but fear its too late for her to believe me) During the relationship i kept saying i didnt want marriage and kids which she did very much and therefore i said the relationship was only temporary which i regret very much but i also said a few times that if she wanted me i was hers forever and sometimes joked about the possibility about marriage and kids. She broke up with me because i was horrible to her and i lost her trust. Since then i have been a mess but im better than i was. I have begged her to believe me that i wasnt thinking straight and that i want to better myself for her and change the negative aspects of my behavior and get myself into a position where i can marry her and have a family with her but she just doesnt believe me. She has also started seeing another guy pretty quickly after me but im sure its a rebound. She did really really love me and I her. Soon after she started seieng someone else she told me it was either that or the nut house. More recently she said she was confused and emotionally distressed and expects the worst all the time. I know i have really hurt her. Talking to her since has been up and down. I havnt really been able to stick to no contact for very long. Somtimes we have talked friendly for a bit and made jokes other times i have been emotional and she goes cold or breaks off completely. The longest was recently for about 8 days then she contacted me and we texted friendly jokey stuff for a few hours and i spoke about how im applying for jobs and continuing for university which i know she wants me to do but probably just as a benefit for myself. Then a few days later I said im so sorry for hurting you we really did have something and she replied with I do miss the sincerity of our lost love i cant deny that but i deserve better than the rejection and lies and mood swings im sorry i cant go back. Im 99% sure ive ruined it too much and theres no chance now and it has been going on like this for 10/11 weeks. Is it too late to start the 5 step plan? She just wont just believe me that ive released alot of things and want to change and sort myself out get a decent job and one day marry her and have a family. She wanted to change me and feels like she failed and is trying to move on and thinks taking me back is going backwards. Sometimes we have friendly texts but more often than not its cold and short. Why doesnt she just say stop texting me? I know that mostly i made her happier than she had been in a long time she said im the funniest person shes ever met and i know the sex was amazing shes said that lots of times and we both admit there was a real connection there, the likes of which she has never had before, but maybe the negative aspects of my behavior in the last few months outweigh all that. She gave me a few chances and i kept screwing it up, she never did anything wrong. There is alot more i could say but hope this is a good enough picture. What should i do? i really do love her is it too late? should i try the 5 step plan or move on? please any advice would be greatly appreciated I can answer any questions if need be please someone help me and thank you for your time