Step-Parent-Open Adoption?

[mdquestion]

I live in MD and have a 13 year old daughter who lives with her birth mom and stepdad in TX. I have always paid child support, maintained phone contact, and periodic visits (4 Xs/year) for her entire life. We never had court ordered custody/support arranged. I just sent support because it's the right thing to do. I did make sure that I had proof of paternity in case anything happened to me so she would have access to my inheritance. My daughter and I, despite a very negative influence by her mom, have maintained a very close relationship, despite the distance.

She recently has expressed interest in having her stepdad adopt her and has stated that it will make her feel closer to her nuclear family (completely understandable) and that she feels it might even "improve" our (her and my) relationship. My concern is less about custody/child support (I'd pay it under any circumstances-- she's my daughter.), and mainly about access to communicate or visit her.

I can't find anything on open adoptions of teenager--just infants. Does this concept exist? I know TX statutes have nothing (for/against) about upholding visitation agreements. I have expressed to her stepfather, a really great person (Her stepmother makes no effort to communicate/collaborate.), that I'm not completely opposed to the adoption if it's really my daughter's desire (at my daughter's age, I'm kind of damned if I do, and maybe damned it I don't)-- I just think it's very extreme to completely cut off contact when I've been a part of her life since birth. I guess I've come to realize that a real dad will support his child even when she's driving a knife through his heart....

To complicate matters, my daughter has a 6 year old sister living in her household in TX and my wife an I have a 1 year old son and 2 year old daughter in MD who are among those who are/will be impacted.

Any info. about stepparent-open adoptions in TX as a possibility or other compromises would be greatly appreciated.