Confused About a Recent Breakup

There are a couple of things that I see in your post that I think I can shed some light on, based on my own limited experience.

As for "are a lot of lesbians like this", there are two things you might know by now:

1. Lesbian relationships can become emotionally deep very quickly.

2. Women are often more quick to break up when things are going merely "fine" or there is the first sign of an incompatibility than a man would in a similar relationship (probably because we tend to invest more of ourselves in it).

However, I can also glean this much about your specific circumstance: there was something your girlfriend either didn't want or was afraid to tell you, and after 5 months she shouldn't have broken up with you over text.

As for what this precise thing is, I don't know, and unless she tells you later you may never know, and unfortunately this is the case of many breakups.

You mention that after the first time you had sex, she asked you about a polyamourous relationship. From my experience, most women don't want this. But also like I said, lesbian relationships can become emotionally deep early on. It's simply our nature, and the nature of women. It can be the best thing about a good relationship, but it also opens the door to a lot of heartbreak, equivalent to what a woman might more likely feel after losing a boyfriend she had been dating twice as long.

Was this the first serious relationship for either of you? I think - and I'm just guessing here - that it's likely she had been uncertain how she felt about you in a romantic, sexual aspect. This could have started before you became intimate. She could have even been hopnig that having sex with you would clarify her feelings. But afterwards, she realizes that she isn't "in love" with you enough to commit to a longer relationship. Because she cares for you as a person (emotional depth!) and likes having some kind of relationship with you, she proposes polyamory to see if she can explore other sexual partners without losing you, so to speak. But you reject that, as you have every right to, and she ends it.

Like I said, this is just a guess. I think that after five months, she should have broken up with you face-to-face. Maybe she thought her reasoning was too hard to say, or too hurtful. It's very hard to tell somebody you're not attracted to them. I think most people would rather be told "I just don't think we'll have any lasting chemistry" than be left to wonder. But she didn't tell you, so there's no real way to know, and that isn't any fault of yours.

So, to answer your question: no, most women do not just up and leave; but lesbian breakups hurt hard. But relationships are also wonderful. I think there was some incompatibility here on her side and that she just isn't the right girl for you. If anything, work on taking things a bit more slow and being more self-sufficient in your next relationship. You sound like a loving and empathetic person, and there's no reason to give up.