I think Raphael has been very helpful, but I'd like to add a little, and see where my own insights lead. I've studed a couple thousand relationship narratives, written a textbook on love relationships in which I developed a stage model based on research, and done couples therapy for 40 years (but part time).
1. 3-4 months is the normal time for casual relationships to either end or become serious.
2. Backing off to spend more time with her friends is a very normal reaction, esp if your frequency of time together had been increasing up to her visit in FL. Furthermore, spending time away often leads to a realization that something's not right with the way one's life is going--tho that doesn't mean that one can discover a better way to balance activities. Needing Space is a very important theme for women in relationships, because they were not brought up with a realization that they would need time to themselves even if they were moving along well in a relationship that looks very good for eventual marriage. Women have typically learned that willingly absenting themselves from their boyfriend or husband is something they should feel bad about, and blame themselves for--so when they feel the need to get more right to alone time and time with other people, they may look for an excuse to make it happen, or actually get trapped inside between their guilt&insecurities about denying intimacy to their BF or husband and their feeling cramped and stifled (because in her case she suddenly got 5 days with NO expectation that she had to be with you--and suddenly discovered how good that felt, and how relieving). And between those two negative emotional states, her excitement & enjoyment of you and your love got all muddied up.
So she appears to be opting for "let's go back to casual" except that nowadays there's a new category for that called "friends." And you can feel that "friends" is living a LIE: It's her solution to an intolerable emotional snarl inside of herself.
Now you're 30, and perhaps quite ready to go all the way to the altar, because the age 30 transition typically involves discovering and deciding what to do that is worth getting older from now on--called "getting serious" and committing to middle adulthood. Hopefully you're committed or now committing to a career that you're willing to sacrifice for, and your attitude toward your GF is that you're willing to sacrifice some of your desires IF you think she's going to come around to continuing the deepening of your relationship--and that DEEPENING has just BARELY BEGUN.
So I suggest you take stock of where you are in life and where you're going (or hope to be going) in the next few years. And do the same about her. Are you getting ready for marriage and parenthood? Is SHE? If she's not a college grad and you are, then she might be more eager to marry a good man (that looks good to her family) than if she IS a college grad and is working and has career goals of her own.
Just from what you've written so far, the key here is what your trajectories with regard to marriage are at this time. For 24 is pretty young for an educated woman to be heading for marriage unless she has NO professional aspirations beyond where she is now, but 30 is on target for a man, whether college educated and professional or more trade-educated.
The "space" attitude is quite different for men too, because we're not usually even aware that "space" is a need that we have. For normally we'll do ANYTHING that seems to be in the interest of furthering our career without even a pause to wonder if our GF or wife would like losing that time with us or not. And if you've outgrown any previous inclination to adventuring (sports, outdoorsmanship, travel, etc.) and/or drinking&partying with "the buddies," then you don't have the competing buddy-networks that don't want to let you go ("and another one bites the dust") the way 16 to 26 yr old guys may still have--or continuing heavy drinkers or adventure-devotees may still have at 30 and beyond.
So she might be calling a halt to your deepening stage, because she's suddenly aware that 1. she doesn't want to get married within the next year, and 2. she doesn't want to feel like she's hurting your feelings every time she doesn't want to be with you. If #1 may be the case, then you've found out in time to assess her life trajectory, and if it seems to be true, you can ask her--better by email, so she's not caught by surprise, but can think it over before answering you.
You could also include in that written communication a few questions about her past relationship experiences. Have you two ever talked about that? It's very wise to do that, tho often people wait until this crisis you're in right now forces them to examine each other's goals--and I think Raphael was focusing on some of that too. "Have you had any long-term relationships in the last 4 years? How did they turn out? Are you worried about me becoming too intense about being together, and perhaps possessive?" If for EITHER of you this is your first new relationship after a long term love that ended within the last year or two, that one might have moved rapidly into this relationship because it felt so good to soothe the wounds and worries about oneself that came from that ending. If SHE's actually done that with you, then it's quite possible that she's just had the time to realize that she doesn't know you enough as YOU, but rather as the kind sweet guy who's just naturally done what she's needed to feel better after her wounding in a big long past relationship-- such as a love that finished thru college but stumbled and crashed before marriage, or a love that lasted for several years since the first time after high school when she was hoping HE would be THE ONE, so she'd gain the summit of the noncollege-woman's aspirations, to MARRY the RIGHT GUY. And what about YOU? How does your relationship history affect your goals and feelings at this time?
THis kind of understanding of both relationship history affects and age- and career- and parenthood-related influences is almost unheard-of among couples counselors, any kinds of therapists, or any research psychologists, (because they don't deal with individual nitty gritty issues between intimates).
I'm bringing this up, because if you are able to consider carefully where you are in your life trajectory and where she is too, then you have a good chance of finding out if you're on parallel paths that could readily converge and stay merged (IF you don't discover some irreconcilable differences that typically don't emerge until 6months or later) or NOT. And if you're NOT in sync in your lives now and in the next 10 years--when you may want to be settled-down and steady & growing children, but she may NOT for another 5 yrs at least--then YOU can make your own decision about whether you want to continue to deepen or not, and you will still be hurt, but not feeling helpless as you do now.
IF she could really be ready for marriage, and IF it's not just your feelings that are driving your relationship, but also your reasonable likelihood of a happy & mutually satisfying future together, then there's a good chance she'll get over her need to back off this much once she finds out she doesn't have to feel bad about doing it. For if she's not had a respected RULE in this relationship that allows her to stay away for a few days here and there, and not to have to immediately promise when she'll be back to be at your side--and IF she learns that YOU also know how to enjoy YOUR alone time and/or your time with other people. Then the problem of Space can be solved.