Well, that's the beauty of falling in love, I think? Even if you need to part one day, the time spent together is still a blessing of an infinity of love and happiness.
For example, my mother and my father met when they were 17. They fell in love, started dating two months after their meeting and married seven years later. They built a life together, had kids, a dog, a house.
Sadly, my father has passed away 13 years ago now. He was only 55 years old. And my mother still loves him and lives with the many memories they shared together.
For me, that's what love is all about. Of course, death is scary and painful. But when time passes, the suffering dulls itself out and you just stay with all of the life you have created together.
If they kept going on to the future where one one of them would hv to part, I would hv cried. Growing old together sounds wonderful but scary all at the same time. Like honestly, how does one live knowing the love of their life would leave them someday because of time? I know these are some heavy things but reading manga's like this always get me thinking about this. Now I just feel like crying （/TДT)/