Sisters" star Tammy Slaton got left in the dust by her on-screen boyfriend, Jerry, after revealing she was pansexual -- but the guy didn't dip over that ...

Jerry seemed especially dumbfounded Tammy said she'd date a transgender person.

Not only did it upset Tammy, but viewers were left wondering about the timing -- y'know, since Tammy had just come out and been honest about her sexuality earlier in the episode.

who tells TMZ she found out about Jerry's relationship with Tammy through TV and friends -- which came as news to her when she first learned about it, sometime during season 1 last year.

Jerry tells us his issues with Kia still make it difficult for him to be there for Tammy the way she needs