There is no common law marriage in Florida. You also cannot enter into a contract based on an exchange of sexual favors. Under Florida law, if you are not married, then as the mother you would be the natural guardian with primary residential custody and control and all the rights. If you wanted to formalize your co-parenting situation, you would need to file a lawsuit to establish paternity and custody/timesharing rights for dad as well as child support. You would be SOL in terms of any alimony or spousal support if you decided to break up again. I don't know what your reasons are, but if you are planning to become financially dependent on this man, you need to make some other outside arrangement, in my opinion, where he gifts you with some sort of lump sum amount of money so that if things don't work out you will have some sort of financial stability. You would be advised to draw up legal papers making it clear that it is a gift. He might also have tax consequences for this. You might also want to both get independent legal advice, and you might want to take the premarital counseling required before getting a license in Florida even though you don't plan on getting married. There are some benefits to not getting married but there are some major pitfalls as well, and you want to be very mature and very clear on what you want and the potential consequences before you make this kind of momentous decision, especially when it may have lifelong effects on one or more children.
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I'll add to Ms. Morcroft's excellent advice that you need to understand that, legally, you'd be roommates. You get no rights pursuant to Florida divorce law, there is no palimony in Florida, and you'd never become common law married so long as you live in Florida. You'd also lose benefits like filing taxes jointly or, in most parts of Florida (but not in Tampa, where you could register your relationship, and where I see you posted from) to visit him in the hospital if there were an accident. Of course, I'm not trying to talk you into marriage; I respect your decision not to get married. I'm just trying to point out some concerns. Call me, if you like, and I'll help you with the appropriate paperwork you probably should think about.
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