Bakit gusto mo siya ba?  mo ba siya gusto?

Ahh, "Bakit? Bakit gusto mo siya ba mo ba siya gusto??".
Hindi ko alam,
siguro dahil mahal ko siya?
Hindi bakit ganap ko alam. ko talaga alam bakit : /
[ paumanhin kung ang aking ng tagalog ay masama hindi maayos. ]

The English translation would be quite helpful. I just translated it this way based on the punctuation you used. This is how I read it in English.

Why do you like him/her?

Ahh, "Why? Why do you like him/her??"

I don't know, maybe because I love him/her?

I don't really know why. (Although I was thinking that you may have also meant "I don't completely know why" in which case would be translated as "Hindi ko lubos na alam kung bakit."

Bad Tagalog skills can be described as "masama" although it's super rare for someone to say this I think because masama is usually like evil or terrible in our context and we use it more often to describe other things.

You'd be better off saying "Hindi maayos" (not ok), "pangit" (ugly/bad), or "medyo alanganin" / "hindi kagalingan" (not too good).

Bakit, gusto mo ba siya? 

Ahh, "bakit, gusto mo ba siya?"
"Hindi ko alam."
"Siguro hindi mo alam dahil mahal ko siya, ano?"
"Hindi ko talaga ganap na alam."  : /

[ paumanhin kung ang aking tagalog ay hindi kagalingan. ]

Tip: Next time, try to include the English translation as well because the sentences sometimes tend to be misinterpreted. Okay? :)

- Teacher Bubbles 

Bakit mo siya gusto ? Or (Bakit gusto mo siya?) (I guess both are fine)

Ahh, "bakit? Bakit mo ba siya gusto ??".
Hindi ko alam,
siguro dahil mahal ko siya?
Hindi ko ganap na alam kung bakit (mahal ko siya). : /
[ paumanhin kung ang aking tagalog ay hindi kagalingan. ]