Can someone help me figure these girls out?

I’ll start by saying I am a pretty introvert person: I don’t get to know other people easily (in fact, it’s one of my biggest fears), and when I do, I feel like I can’t build any strong tie with them. I’ve had three relationship in my whole life- the last one was very short. I broke up with my ex gf in November and started seeing this new girl who’s been interested in me since day one in college. She has been hitting on me, acting jealous and all, she wanted me to break up with my girlfriend and I did, once I realized I had feelings for her. I felt it would be disrespectful not to tell my girlfriend I was interested in someone else, and I couldn’t figure out who I truly loved at the time, maybe none of them.

Thing is, as soon as I was “available” again, she seemed to lose interest. She started not answering my texts for a long time. Since she has a pretty severe illness, I respected it and tried not to get in her way, but she later accused me of ignoring her. She was convinced I would cheat on her with my ex or any other living being (of course I wouldn’t) and in the end, after we spent a night together, she broke up with me saying that things weren’t working out, but she wanted to be my friend anyway.

Meanwhile, my ex texted me, and I started to miss her, but I tried not to make her a scene, since she made it clear that she didn’t want to come back together. I didn’t actually get what she wanted: she often texted me first and got angry if I didn’t answer in a short time and things like that. On Christmas Eve I told her it was difficult for me to keep it going since I was missing her terribly and getting very confused, and she started insulting me, stating that I had to stop bothering her and get a life of my own. She then deleted my number. I didn’t look for her again, but four days later, she texted me again with an excuse, I kept things cold because of what she told me that night and then after a little bit she deleted me again. When I asked for explanation, she told me it was none of my business so I left her alone again, more confused than ever. When she texted me, she used to say she immediately regret it. But why should she text me then? I was very in love whit her and ours had been a difficult relationship, so neither I could figure out my feelings, nor understanding hers.

On New Years’ Eve, I was chatting with the “college girl” on Instagram. It was easier to maintain some sort of friendship with her since I understood, with time, that even if I liked her, my feelings weren’t as strong as when I am truly in love. We were just joking around as we did since she said she didn’t want me, but then she started teasing me saying that she saw my ex found a new gf. I should have known she was lying, but in the heat of the moment, I believed it. I got angry, yes I was feeling jealous but I was mainly angry because my ex was still texting me, bothering me and making scenes as I told you, so I thought that if she did find a new girlfriend she should definitely leave me alone. Seeing my reaction, “college girl” got angry, saying that I was still in love whit my ex (possible, but I mean, she was the one who wanted to be just friend, so I didn’t think she had a right to judge what I was doing or feeling). She didn't know anything about what happened between me and my ex on Christmas.
She thought I was texting her on Instagram as my ex would get angry at me if she saw me online on whatsapp, which wasn’t possible since I didn’t get back with my ex gf. In fact, “college girl” was the one who preferred Instagram so that was why I used it. But she was convinced of all this lies and later on blocked me. I didn’t make a big deal out of it, but it still bothers me as I don’t understand.She was also my only friend in college.

Now, I know it’s only two girls, but, given the fact that I’m really not good at finding new friends or potential girlfriends I’m starting to worry: am I the one who’s making mistakes in these relationships? Did any of them wanted me back despite saying they just wanted to be friends, and was all this a weird way to show interest? Maybe they didn’t want to show it? Why can’t I figure out what other people want or think? Oh, I’m 20 yo if someone was wondering. “College girl” is 26 while my ex is 21.