Daww great start! Thaddeus is adorbs. Two bits of wisdom I can impart onto yah -
The ridiculous muscle-gain comes from digging rocks. The system is broken atm so that after 5-6 rocks you're sim is suddenly a hulk with a maxed muscle-bar. You can fix it through the testingcheats on/full.caseditmode cheat (but beware, some have reported that it messes up familial relationships if you have more than one sim in the household at the time of using it). There's also a mod out right now that can disable muscle gain and/or thin-to-fatness gain. I use the muscle one specifically for my collector sims.
The reason Candice turned down poor Thaddeus, these 'weirder, smarter' sims apparently are smart enough to realize that proposing 2 sim-hours after you became a BF/GF is kinda stalker-creepy and they'll reject it every time, lol. I learned this in my own legacy. It's best to wait 24 hours at least after the initial relationship is made before you go for the ring.
Good luck in the future! I'm looking out for updates.