Me [22 M] having boundary and communication problems with my fiancée [24 F]

(Background)

My fiancée and I have been engaged for five months, dating for two years, and have been friends for four years. We were the best of friends in college and then I finally got the courage to ask her out a month before she graduated.

We have had a nearly perfect relationship. We have the most fun together, do almost everything side by side, seek each other's guidance, and plan our future together. We get married in seven months.

I'm about to finish my undergrad studies at uni, while she has been out of school for almost two years. Most of her friends have moved away and she does not get along with her housemates, so I'm essentially her main friend left. I absolutely love spending time with her and I have no doubt in my mind that this is the woman I want to spend the rest of my life with.

Years back, I was diagnosed with acute social phobia and depression. It was wrecking my life to the point to where I couldn't go out in public for fear of...I don't know. I never knew and still don't. But it was the worst feeling. I would become depressed easily, even though I'm blessed with so much. I eventually saw a therapist, was prescribed medication, and took steps to get my life on track (working out/gains, etc.) My fiancée knows all of my history and has always had my back, listened to me, and comforted me.

(Present Day)

As we prepare for our wedding (we're fairly young for the national average, but when you know, you know), I'm becoming stressed and depressed again. There is so much money involved, it's a monstrous step in life, and I am fairly flatline, I like things to move slowly and smoothly. My fiancée has been in charge of most of the wedding details and is trying to complete EVERYTHING all at once. I've tried to get her to slow down but she gets too excited and then gets upset that I'm not as "into it" as she is. I also value my alone time very much and I have times where I literally want to disappear for a bit and relax on my own. Even though we've discussed it, she doesn't understand why I want this and I have trouble expressing myself. Example. Tonight we made dinner and watched one of our favorite shows. It was still early and instead of spending the night doing something together before the week starts, I want to go home and retreat. I have these weird waves of sad feelings where I just want to get out of a situation, even if it's perfectly happy and fine. So instead of explaining myself (which I CANNOT seem to do) I tell her I want to go home. She gets really sad and upset that I don't want to spend time with her, why won't you talk to me, what's wrong, etc. And nothing is inherently wrong, I just....gah it's hard to explain. I hate it. So now she's a bit mad at me (we still told each other I love you, goodnight, our usual) but I can't help but feel either inadequate in being with my fiancée all the time or feel like she doesn't understand me as much as she thinks she does. We usually have extremely open communication channels, they just get locked up by bullshit sometimes. I'm sad and I know I won't stop being sad until we compromise. How do I explain these weird feelings that will undoubtedly continue throughout our marriage without hurting her feelings? It may not be "coming through" right but those of you who have had even slight depression might understand.

tl;dr: Can't explain weird, depressed feelings to fiancee, can't decide if I'm being too jealous with my alone time.