should i give up my 16 year friendship?

My 2 best friends are brothers, and the one is engaged and the other just got into his first relationship.

I know how this is gana end at the end of the day I will fade into the background and eventually left behind as they move on with their girlfriends and i do not have a girlfriend. I personally think i should back off from their lives and move on with mine.

I am happy for them that they found someone. but now that they have someone it kinda feels like i do not exist anymore and that i am always putting effort in. Honestly i am tired of it.

They have been there to me and i them. something just tells me to move on.