(Diclaimer: non-native opinion) Well, בְּמֶ֫שֶׁךְ כׇּל הַחַיִּם שֶׁלִּי sounds fine, but often the בְּמֶ֫שֶׁךְ is left out, forming an adverbial accusative: יֵשׁ טָעֻיּוֹת שֶׁמְּשַׁלְּמִים עֲלֵיהֶן כׇּל הַחַיִּים There are mistakes one has to pay for life. This is already old biblical usage: ועפר תאכל כל ימי חייך Gen 3.14 and you will eat dust all the days of your life.
Well, I would say that בֶּן־זוּג or partner means a more serious, long term or permanent relationship with someone, somebody you plan life with until you die, while at the same time it has a progressive ring of people not interested in traditional marriage, but חָבֵר or boyfriend is someone you go out with or when you still try to figure out how well the other person fits to you longterm.
Thanks for your help. One last question: Duo teaches us that חבר means "Friend." So if you say boyfriend, then it seems that the context in which that word is used will determine whether it is someone new in a relationship or if they're talking about a friend that is male. That's my understanding at this point.