Struggling to Express Myself Without Starting an Argument

i expressed my feelings and it started an argument…. i’ve always had a hard time expressing myself to the point where it has to be really really prevalent for me to end up expressing them, especially to the person it involves and even when it gets to that point i’ll often underplay it because i don’t want to make them feel guilty or hurt them. when i would express my feelings to some family/friends it would most often turn into the blame game or throwing back something that i’ve done. so now i just try to avoid this issue, well now i expressed my feelings and it’s turned into an argument that i didn’t want. i told my bsf after she rescheduled again that we’d have to put off hanging out another week if she can’t this week (because she has a test coming up) since i have my next term next week and the first week/last week are always super busy and because i almost failed my last term i was nervous and tryin to really focus this term. i don’t think i sounded passive aggressive or annoyed (even tho i am but not at her having the test, at the constant putting off the dates) she she said it felt like I feel that she is dodging me or that maybe she was reading it wrong, I did tell her that it does feel like she is dodging me, but it’s OK. I don’t want her to feel the test so we would just have to put it off another week because I also have school. she then threw it back into my face basically, and started saying that she would never get mad about me being late to hang out when we would always go to her house (we always hang out at my house now) and she shouldn’t feel like hanging out is work and she shouldn’t feel guilty about putting things off. but the thing is I never make any comments about her being late or pushing off the dates. The only thing I’ve ever said is hey if you’re any later, we might have to put this off because I have homework due tonight or like I said earlier that my term starts in the 1st/last week are always the busiest etc. I would never make sly comments or anything like that, but for her to just throw it in my face and make me feel like I’m doing something wrong for expressing that I do feel like she’s dodging me. I just responded her to her that I don’t want her to fail the test. I was just letting her know that we would have to put it off another week & although I do feel like she’s dodging me because anytime it comes to a day that we’re hanging out she always puts it off or moves it. I also said that it feels that she doesn’t even really want to hang out with me because if I don’t text her we don’t hang out, I am always the one reaching out to hang out. if I let things be and wait for her to come to me, we wouldn’t hang out or if she did text me it would be about some thing her child’s father did and how annoyed she is and how she’ll tell me when she sees me but never make plans and I’ll have to make the plans and then go into the cycle where she doesn’t show up. i don’t want to make her feel bad or make her feel that she’s doing anything wrong, but i’ve let this go unaddressed for so long now and at this point all i really want is to see my niece, i love to hang out with her but these feelings have just been building up to the point that i don’t even care to see her all that much because it doesn’t feel like she actually wants to hang out and more so a way to shut me up. but anytime i express my feelings and something like this happens i always feel like i’ve done something wrong…