First off, I'm glad you cut contact with him. If he's this flaky in three months, I'd hate to see you spend another day with someone like that.
And that's probably where my niceness is going to end. As a woman and parent, I can't understand what or why you're acting like any dick will do. You put your safety, and the safety of your child in the hands of a stranger. Yes, a STRANGER. You have to be better than this.
Anybody who says they fell in love in three months time doesn't know what love is. You should have run for the hills the first time it came out of his mouth. What you experienced from him was lust and loneliness, not love. And you fell for it, hook, line and sinker.
As a parent, you have an obligation to your child to raise him/her in a stable environment. That means, you don't bounce men in and out of your bedroom and the child's life just because you are horny. I like sex, sex is good, but my child always comes FIRST. From your post, being a parent is a side note for you.
I'm not going to get into the reasons why he dumped you. What you should be doing is thanking your lucky stars that you dodged a bullet with him. You need to start thinking more seriously about your actions and how it affects your child.
I'm not saying don't date. I'm saying take some time to get to know who you are dating before moving him in to play pseudo husband and father. If after a minimum of one year (maybe more) and it's a good fit for everyone involved, then discuss cohabitation.
As a single parent, run a simple background check on somebody you're dating. A simple search in the county of record Clerk of Courts for drug related arrests, prior domestic issues, prior marriages, driving record and bankruptcies are all public record and a NECESSITY to ensure you know who this person is. You don't need his permission or social security number, just his full name. And if a man balks at you ensuring your own safety and your child's safety, then he's not a good candidate for you to bring home.
Start thinking with your head, not your vagina.