I met my first real boyfriend when I was 18 and we were together 14 years, then we broke up as partners but stayed really close friends even though we lived in different states and each had other relationships, up until now, so it's been 41 years. He broke my heart a year ago and it's been terrible, but I will always love him more than anything in the world.
I don't really understand the concept of serial monogamy. When someone becomes my long term partner and I love them with all my heart, they are a member of my family. Even if we break up, they are still a family member and I still love them. It doesn't take away from the love I have for my new partner, who is also now family. I don't understand the concept, which is usual, of having a life partner and then ditching them and they are just gone from your life. How is that possible? How do people do that? That would break me. (If they did something terrible I get it, but only if it's bad enough that it's unforgivable.)
Also, I miss people horribly when they are not there, if it's someone close to me. It's like I can't tolerate their absence.
My ideal is to be with my partner 24 hours a day. That's how it was with the boyfriend I mentioned above, when we were together for 14 years. Except for work, but neither of us worked full time.