Resentful feelings

Long story short my mom and I overall had/have a fantastic relationship. Shes super supportive, helpful, encouraging etc...For some reason that I cant figure out I have such resentful feelings for her, when she calls I cringe, when I see emails from her I cringe, a phone call with her is literally something I dread every day and I dont know why. This doesnt happen in person with her. We have been to counseling together, individually, we have talked to eachother and hashed out differences and nothing works. There are two things that happened as a kid that I still think about and blame that as the reason I feel this way today. In 8th grade I was approaching the graduation dress shopping time and was so excited for my mom to take me and it seemed like she kept putting it off then one Sunday she asked me to go and I was so excited. We left my dad and sister at home. Once we got on the road she told me we werent really dress shopping, she was bringing me to meet the man she was having an affair with..... and she did, and I met him and was polite but inside i was dying. I couldnt believe she would 1. have an affair 2. make me meet him. So many emotions were running through my body. After we left there she didnt even take me dress shopping. We returned home and I kept that a secret. Later on when I was 15-ish I was dealing with my first serious relationship and it was an unhealthy one. There was absuse, mind games, just horrible and that was hard on me. My mom left my dad and took me and my sister with her. We were staying at my aunts who was away and my sister went to a friends house so it was me and my mom. She left to go out to the bars and hang with men. I was in need of her, my parents just split up that night, my bf was abusive, i needed her and she wouldnt respond to her pager. I paged her 911 and told her to come home i needed her and she said she would come home when she was done. I sat there w/the worst depression and feelings ever. She did this one more time to me, she had gotten back w/my dad. I was 17 and was in another relationship with my first true love (to this day he still is my first true love)and it wasnt working out so this was my first love breakup which as we all know is devastating and my mom left my dad again during this time and again was out all the time when I needed her the most. I was never close to my dad (until the last couple years) and so this was really upsetting. My mom has since acknowledged what she did was wrong, and apologized and for some reason I just have deep resentment for her and I am assuming it comes from these two times....BUT on the other hand when my mom and dad finally divorced my dad came forward with admitting his affair that happened long before my moms affair and was w/her best friend and I hold no resentment towards him. He wasnt there for me ever, he was never a good dad, he was a jerk to everyone yet I dont hold resentment towards him. My mom grew up dealing w/being raped over and over and abused so I know she struggles w/life and I dont want to feel this way towards her especially cuz she is a good person (now). She now suffers from anxiety, depression, bipolar, has emphysema and COPD and I just constantly feel like I am her care taker and have been her parent throughout everything. She is super dramatic not even on purpose, I could tell her something as simple as I found 10.00 today and shes going to call up 5 people to tell them and add things to the story and make it huge when its not. She is aware I feel this way and we try to talk abt it a lot but I cant seem to get better....any suggestions?