Inside Japan during the 180 days temporary visa reset

You'll be fine. On entry into Japan, you will be granted another 90-day Entry Permit, and you can legally stay in Japan until that expires. And since there is a respectable multi-month gap after your previous visit, you will not ring too many alarm bells for being a "visa runner".

All that said, two very lengthy trips for tourism will start to raise suspicion, if not this time, then almost certainly the next time you try to return to Japan. Be prepared to show evidence of how you're funding this trip (= you're not working illegally) and evidence of family ties or other strong reasons to leave Japan (= you're not planning to overstay). I would also strongly encourage you to find work in Japan, perhaps as an English teacher, so you can legally stay there for a longer period and make some money while you're at it, and start thinking seriously about what living together with your loved one would entail -- one of you will have to move to the other's country if you want to pull this off.