Your fears are not unreasonable, but it might be worth seeing if you can get over them. Nothing spoils a good time as easily as worrying about when it's going to end.
And make no mistake, all things end eventually. At the very least, you all have finite life spans. In all probability, 1 of you is going to lose 3 of their loves. I keep hoping that my husband and I will go out in a blaze of glory, a really spectacular car crash involving no other vehicles... of course, not for a long time off... but at least some point before either of us loses control of our bowels or forgets who the other one is.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker