Can i save my relationship with my baby mamma/gf/fiance?

over the past few months things have really started to go downhill, she shut me out, said very little to me for almost 2 months, i would ask her again and again whats bothering her, all i could get was, she was stressed, and she had cabin fever (she has no car or way to go during the day while im at work and shes with our son), so to do what i could i gave her the car when shes wanted it, her behavior got worse she went from shutting herself off to opening up a little bit, she spends most of her free time that should be with "her family" texting back and fourth with some girlfriends, keeps her phone pword locked. she wanted to get a ride home from work from a friend on nights she bartended at work since i always complained about the long wait in the car, so i agreed she then wouldnt come home untill 4 in the morning when she gets off at 2..., another day, she was having a "bad day" so she then took off by herself to get drunk and left me stranded at work, didnt answer phonecalls or texts, called me an hour and a half later than when she should of picked me up drunk as a skunk, and then 2 hours later ended up home. most recently we got in an arguement she decided to leave the house, never returned the next day, came home 2 days later to find i had changed the locks (i was angry..) and left for another 2 days, not calling me to let me know she was even alright or alive, and leaving me with our son and him with outhis mommy. we have a stressful life, we are both young parents both work 40 hours a week, have a house payment, and she also is a part time student. but this behavior has to end...i have been more than patient giving her room to breathe, trying to help where i can and even sitting her down and saying, maybe you have reached your stress point and need to talk to someone to get sorted out or vent, maybe you need to see a doctor..which she agreed could be a possibility to why shes all crazy. she doesnt want out of our relationship she wants to fix it, but when i ask what i can do to help she says its all her, the one thing she requested was the car when she wanted it and she got it. ive stood by as a good partner when if it was the other way around she would of gave me the boot a long time ago at the start of all this hijinx, im at my wits end and im just looking for advice, and wondering if i can save my family...i need help!!