Edit: apparently my account is too new so my responses to comments are getting deleted, oh well.

I'm 25 and have been with my FH for \~6 years. I dated a couple guys casually before being asked out by FH during my first year of college. He sowed his wild oats his freshman year/most of sophomore year, got disappointed with shallow sex, and then asked me out. I'd gotten crushes and butterflies in the past, but nixed other guys on account of basic incompatibilities re: religion, values, etc. I didn't really "fall" for FH, but liked him, respected him, and eventually loved him. He's my first everything. There was an intention to hold out "real" sex until marriage on my part, but that ended about nine months in (tmi, but perhaps related to my current fomo). We're good together and compatible on all the major issues. He's awesome, driven, handsome.

5 years after we started dating (including 3 long distance), I moved jobs and we were finally closer. He proposed in early summer, and two months ago I left my apartment and moved in with him. Initially I was opposed to cohabitating before marriage, but his job pays for his apartment (so much money saved!). Also, he was pretty adamant about living together.

I love him, but I'm having a hard time getting excited for the wedding and also the marriage (a tiny bit). I'm applying to go to grad school right now, and I'd always imagined already having that degree before being married. All my friends are single or going through breakups. On one hand, I see how miserable they are trolling Tinder/Bumble. On the other hand, I've never been single as an adult. I'll never get to feel butterflies with anyone else. Wedding planning holds no appeal for me; I suggested eloping, FH and my mom want a big wedding. I don't have a ring, which is fine, but means I still get hit on occassionally and think, "what if...?" Then I remember I'm engaged and feel guilty. We still have sex (I initiate sometimes), but I feel emotionally closed off and FH notices.

I talked to therapists after getting engaged, and they were pretty much puzzled as to why I was sad in a great relationship. Even the more progressive of the two therapists affirmed that it's hard to find an excellent man before hitting the early-thirties scramble. I've been trying to "glow up" and eat super clean in anticipation of pictures/wedding dress shopping, but even when high on exercise endorphins, I still feel sad.

Basically, I should be grateful and excited. So why am I not, and what can I do?