Please. Stop. Stepmothers don't and shouldn't have rights. It's not your kid, have your own and let your husband take care of his. Quit being so insecure that you have to put down bm or overstep. If you and him divorced, you wouldn't see or put any energy toward your step kid anymore, which is why you're not the same as a mother. Im sick of seeing step moms glorified. Just stop.
Edited add on : to clarify, I am a step mom and bio mom. I don't mother my step son, I am a friend. I've never had issues with his mom, because I don't overstep nor do I wish to. I have my own kids. My step son and I get along great, my ex (who I have one child with) and I get along great. He hasn't remarried yet either.