Firstly, holy shit that speech and his arrogant way of showing off his wealth was so cringy it actually hurt to read. Also it was totally out of character since the mc didn't do/act like that before ever. "I have more money than I know that to do with it".. Yeah nice job not painting a huge target on your head for bad people. If he has so much money, then why is he paying rent? Why not just buy/build their own dream house..
Also damn I hate this trope of the mc being way too forgiving/nice to a fault, when he's first being treated like shit (may it be originally a misunderstanding or not).
Secondly, where the hell that confession came from?? Seriously wtf. It wasn't deserved at all! There simply wasn't pretty much any romantic progression or signs of him actually falling for her, nor any real intimate/emotional moments. (you can barely count the time with dog cockblocking him)
Normally in stories where there is a romance happening, they might have situations where the other one is being seduced by a 3rd party, and by so the other one notices his/her own feelings by becoming jealous. This feels just totally out of the bushes and rushed, and like I wrote before, not deserved.