When is it ok to stop?

Looking in on the situation I'm sure I would say to someone - you have done all you can and its ok to stop, however, when you are the one its not quite that easy.
I don’t know if or when I will ever be able to say I did enuf if this doesn’t work. I would love to be able to walk away from this IVF feeling good about all I have done and even if it doesn’t work, still being ok with what I have done so far but I don’t see that happening, not at all. I figure I will spend months trying to figure out where I can blame myself for doing or not doing something correct when in all honesty I know that I could not possibly do anything else in my power to make this happen, I have spent more time on this than pretty much anything else in my life. I am not competitive, but I am a fighter when it means something to me, like when Harmony was little and no one would listen to me about there being something “wrong” with her. I pushed til I found someone to listen to me. Im pretty lazy when it comes to life, but some things light a fire under my ass for sure.
I do not want to waste my life with “what ifs” but I don’t know how to stop and be ok. I don’t know how to pat myself on the back and move on. How do you pat yourself on the back for a good job when you don’t get what you fought for?
I am not only fighting for myself, I am also fighting for the man I love. I know I have probably talked about this before but my heart breaks every time I reminisce about when the kids were little or I see them doing something that is totally something that is me or Brian. Matt loves the children, its very obvious, but he cant know the love of having your “own” child and watching that child grow up from birth. Its amazing that when you don’t have children you can love a child in the family and you feel sooooo much love for this child but it cant even compare to the love you feel for your own. You cant explain this to someone who doesnt have children, it cant be explained, its just felt the second that your child looks at you. I want him to be able to feel the love that is felt when a part of you is walking and talking and being wonderful and naughty all at the same time. I want for us to share in all the wonderful and stressful times that come with infant-hood. I remember even as hard as life was when the kids were little, Brian and I would always laugh about something during the day cuz the kids were around and reminding us that most days were just exhausting but amusing.
He deserves to have that experience.
Im sure plenty of people “deserve” things that they don’t get, I understand that people with MS “deserve” to be able to walk and not have vertigo,people with cancer totally “deserve” to live a full life without pain and chemo, etc. - I just don’t know how to get past my feelings of failure and move forward without regret or hatered for myself. That is where I get caught up. I talk to the therapist and she helps but its not a fast process, and as everyone knows, I am not the most patient person in the world. Logically, I know its not a failure but that sure doesn’t help to get past the feeling.
I have flip/floped a lot these last few months. This being the last try is both freakin’ me out as well as making me feel at peace (some days). I have been doing this for almost 3 years now. Everything that I do revolves around this so reaching an ending does sound very appealing, however, if that ending is not the one I envision then instead it is scary, very, very scary.
I don’t know where I would stand in all of this if I didn’t have children. I often wonder if I would fight harder or if I would have given up long ago. Looking at those kiddos makes me know how incredible it is to be a parent and how much I want Matt to also know that feeling. It is the only thing I have ever wanted for myself, to be a good mother. I never cared about college or a career, never had big dreams of being wealthy...... only having children and being there for them so I’d like to think that if I didn’t have children I would still fight this hard. On the flip side tho, how could I possibly know how incredible it would be to be a mother if I wasn’t one? Would it be this hard to walk away since I honestly would have no clue what I was missing. I don’t know and thank goodness I never will.