The reason you can't rule out the possibility that things could escalate is the fact that he's done nothing to change his behavior. This mumbling thing is troubling because *unless his IQ is like 70* he has to know there's a chance you or anyone else could hear it -- and you have in fact heard his comments many times now. This is a grown man, who presumably has a job and participated in social scenarios his whole life. He knows what's inappropriate to say and he knows when other people can HEAR him. He may be testing the water to see if you'll say something about his behavior. The fact that you don't say or do anything could be a sign to him that you don't mind it -- I'm not saying that's okay, but that's the kind of faulty logic that happens in people with poor boundaries.

Maybe the weight loss has something to do with it (and congrats on the weight loss!) but it's still not an excuse.

As supportive as he may be otherwise, he's totally fallen down on the job here. You should never feel this way in your own home or with your own family. It's not a difficult task to NOT sexualize your stepchild. So I'd argue he's a terrible parent. You may think he's not the worst person in the world, but he's not a good parent at all.

Someone needs to lay down the law even if it will presumably hurt his feelings -- your feelings certainly haven't been taken into consideration here. You've been treated like a piece of meat and it needs to stop.

Sometimes we see all the good in people around us and that's a healthy way to be, but his behavior is too detrimental to ignore. He doesn't get this special consideration anymore because he's been sexually harassing you.