All we have to go on is what Kelsey's mom said, which was that he was her fiance and they were "loving," and they were planning on getting a home together but the economy wasn't good, or something like that. But we don't know of any formal engagement announcement, and they did not have a wedding date, nor did Kelsey have a ring that we know of.
It was also stated by Kelseys aunt that Kelsey broke up with him Thanksgiving morning, but we don't know if that is something PF told her mom, or where that information came from.
In my opinion, they did not seem like a happy couple planning to marry. They lived apart and seemed to spend time with the child separately. On the day that Kelsey was last seen, the two of them had "exchanged" custody of the baby. Imo