Things I don't like about my friends

Songi wanted to go out with me last Friday night but I was very tired and wanted to meet her next day instead. She insisted that she wanted to meet me that night saying that she went to work and came straight home after work for the whole week and she was too bored. So I decided to meet her. In the afternoon, she texted me and said she was feeling tired too and it would be better for us to meet on Saturday. I was ok with that.
On Saturday, when I woke up in the morning, I found her text that said "I am feeling unwell. We'd better meet on Sunday afternoon.". I was still feeling tired so her cancellation didn't bother me too much.
Saturday afternoon after work, when I was going to Hanaro mart at Mokdong with my sister, Songi called me and said she was too bored staying home all day and I said "We'll definitely meet tomorrow.".
Sunday morning, I was chilling out at home eating some bread and watching TV ("CEO exchange" I really like this show!). Around 12 pm, I decided to call her to arrange the time and place to meet. She didn't answer the phone and my text after the call. She called me back 30 mintues later and said she was out to have lunch with her roommate." As soon as I heard her say that, I knew what she was gonna say considering she was full at the time. She said "I am sick and let's not meet today.". I got really mad at her. She said "I am so sorry. Let's meet on Monday.". I said "I am meeting my friend on Monday. But I don't wanna meet you even though I didn't have a plan for Monday. How could you be so rude? You always do whatever you feel like. If you felt sick, you should have called me earlier. You ruined my weekend." I hung up.
This is a pattern actually. She always does this and I get angry with her. I stay angry until she calls me several times and says she's sorry. Then I have to forgive her.
I don't mind Songi reading this because I complained to her about this thousand times already.
I tried not to meet other friends of mine while Songi is in Seoul. It's because not only I feel most comfortable with her but also I don't want her to feel lonely as she doesn't have many friends in Seoul. Maybe I was too considerate of her.
After Songi's third cancellation, I called some other friends of mine immediately and made plans for this weekend to rule out the possibility that Songi ruins my weekend.
She texted me this morning but I don't want to reply. I can't change the things that I don't like about my friends but at least I don't want to let them affect my life.