So, the MC is good looking, friendly, intelligent, gentle, a genius magic user and the son of a noble and a hero (bastard son, but son nonetheless).
He decided to marry the girl he grew up with, who's cute, has always been loyal and with whom he developed mutual feelings over the years. Understandable.
He then meets an orphaned girl that idolises his mother for avenging her parents' murder, he then cures her incurable diseased body, mediates between the guild and the butler to save her territories and gives her the opportunity to see a world she could only dream of. They decide to marry each other for mutual protection, political strategies and budding enamoured feelings. Perfectly acceptable.
It's kind of refreshing to have a MC marrying multiple cute girls and that it actually makes sense.