How do I keep my bishop pair in this Ruy Lopez line? I am learning Ruy Lopez. And I always play Ruy Lopez opening while I am playing with the white pieces. I recently played the game with Ruy-Lopez and my moves are 

[FEN ""]
[StartPly "10"]

1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 Na5


I want to keep my Bishop pair, but if I play like this then my light-square bishop will be lost in 5 moves. So, what is the best move that I can play to save my bishop pair till the end?
In that position, you can't keep your bishop pair if Black wishes to take your Bishop. Acording to Modern Chess Openings, with this variant Black throws away the White Bishop by ceding the initiative in the center. In the recomended continuations, White has an advantage (+/=) and White must proceed to an inmediate attack:

[Event "Analysis"]
[Site "Ruy Lopez"]
[Date "2020.04.11"]
[Round "?"]
[White "Player"]
[Black "Oponent"]
[Result "*"]
[FEN ""]
[StartPly "10"]

1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 Na5 6.O-O d6 7.d4 Nxb3 
    ( 7...exd4 8.Nxd4 Bb7 9.Bd2 Nxb3 10.Nxb3 Nf6 11.Re1 Be7 12.Na5 Rb8 $14
    {Smagin - Kupreichik, Minsk 1985.} )
8.axb3 f6 9.Nh4 Ne7 10.f4 exd4 $5 
    {It is a possible improvement.}
    ( 10...Bb7 11.d5 c6 12.c4 exf4 $14 {Arnason - Agdestein, Gausdal 1987.
    } )
11.Qxd4 Bb7 12.Nc3 $10 
    {1/2-1/2(64) Alves, Lair Valio - Petters Merino, Oscar Augusto / CLEA4
    B07 email, CADAP Email 2000.}
*