Most Helpful Guy
It's not guys. It's everyone.
Nobody breaks up with someone else until they're ready to move on. Just doesn't happen. This has been coming for weeks, maybe since the very beginning, and you just didn't see it.
Usually, when breaking up with someone, you peter around the issue trying to find the best way to do it, dragging it out while pretending to still be invested. Until someone else comes along that you want to date. Then you need to break up, and so you just make it happen, so you can start dating the new person without looking like a complete ass.
And yes, three months is absolutely enough time to become emotionally invested. I'm sorry this happened to you, that sucks. I've been there (used as a rebound, got really into the girl I was with), and yeah, you feel like sh*t, like you were used.
In reality, it probably wasn't really like that for him. He probably liked you and thought things might go somewhere, maybe even really wanted to feel for you, and later realized that it just wasn't quite working out that way. It sucks, but that's how it sometimes goes. I've been on both ends of the situation a few times, and you probably will be too.