should I fight for him ?

Since he says he will never breakup with gf, you must ask yourself are you/they wanting a open relationship of sorts...if not, stop thinking it's worth it.

I went through that exact same thing for 9 years. Ours wasn't as on and off as yours and we were older when it started, but I always had my race race around him, etc, and it was on and off a few times. He got a new girlfriend, I moved away. He eventually reached out to my friend to get my number because he missed me so much and I never told anyone that my heart was breaking daily not being with him. His ex girlfriend even told his mom that she had to leave him because he was always comparing her to me and she couldn't stand it. We started talking as friends but he told me what a mistake it was ending things with me, how much he loved me and would do anything to have me back. We talked every day for months and months. It was better than it had ever been. That is until the new girlfriend he was living with called me. When I tried to confront him, he just hung up the phone. I was in FL and he was in NC, so not like I could just go confront him in person. After a year he called me. He cried, apologized, told me that he had broken up with her and she got his phone and lied and he thought I would hate him and not believe him. So, it started again, the talking, the trust building. Him calling me every single day and night. He loved me so much. But apparently not enough to end his next new relationship. This one he is now married to. All the feelings, the tears, etc was bs. He wanted to have his cake and eat it, too as the saying goes. I'm not sure if you told him how you feel, but if he poured out his feelings and said he would break up with his girlfriend then you most likely did. If so, then move on, he doesn't love you enough to leave her and do not listen to what a HARD DECISION it is. When you love someone truly like that, there is nothing that would stop you from being with them if they want too. If you havent, then you need to tell him now and give him a week. Seriously, if he loves you that much and he knows you feel it too there is no reason he won't end it like immediately. Another concern is that if he loves you like he does, he knows you are single, then what is he doing? Why didn't he already end things with her when he realized how he felt? He plays games with people's emotions? I'm not saying my situation is yours, but I wish I had really questioned those things and saved myself years of heartache. I literally ached and hurt every day not being with him.
Also, you will never feel that feeling again with anyone. It's because when you are young, you immerse yourself in that person. There is no emotional baggage, no guards up, etc. You lose yourself in them. I am now happily married. My husband is my best friend. He treats me well. He is my partner and my best friend. The feeling isn't as intense but it's different and better. There is comfort, trust, love, respect, and deep friendship in our relationship. Although, I my heart doesn't skip a beat when I hear his name, my love is deeper and stronger than anything else I have ever felt.

1. No Attacks or Insults and No Reciprocation

a) Do not attack, mock, or otherwise insult others. You can respectfully disagree with the message or topic, but you cannot attack the messenger. This includes attacks against the user’s spelling or command of written English, or belittling a user for posting a duplicate topic.
b) If you are attacked by another user, and you reciprocate, you will also be subject to the same consequences. Defending yourself or a friend is not an excuse! Do not take matters into your own hands – instead, use the Report Post link to report an attack and we will be happy to handle the situation for you.

6. No Intentionally Hurtful Posts

Topics or posts which are started with the intent to belittle others, either directly named or through enough descriptive commentary to be possibly identified, are prohibited. This includes stalking a poster through the forums, posting about past events gone sour, divulging personal information, or spreading gossip or rumors. At our discretion, any post referring to the behavior or posts of other users of the site will be removed.

17. No Profane, Vulgar, or Sexually Explicit Language

No explicit, sexual, insulting or vulgar content including expletives, or sexual innuendo, will be permitted. This includes the use of non-alphabetical characters to approximate expletives or other objectionable language. Publicly visible text on MyFitnessPal should be work-place friendly.

We reserve the right to moderate a topic or post based on the intent of the sexual material it contains. Posts intended to titillate will be removed. Posts with medical or clinical themes related to sex or sexual health may be permitted, at our discretion.

Cross the bridge, toss the match on it. If you don't, this is going to keep happening as long as you allow it. Let it go. As time passes, the hurt will fade, but you have to let the time pass. Also, I think you need to expand your social circle. Good luck, sweetie.

If you have to ask this question, the answer is no. Let him make the decisions he needs to make to be fully committed to you. Until he does that, do not invest your heart.