Can new sexy underwear indicate that my wife is cheating?

Has anything else seemed off? If not maybe she just wants to feel sexy. Also sometimes wearing that kind of underwear with certain pants makes it so you don't have the outline of underwear (Like tight leggings or something).

Does it matter if she is or is not cheating? I mean, you're sleeping in separate rooms, no love life and the problem you want help with involves her purchase of new underwear?

You don't indicate if the two of you are wanting to keep your marriage intact. If you are simply staying together for the kids you are doing them a disservice. Trust me, if they are teenagers they know all is not well between mom and dad. You and your wife need to sit down and talk. Either end this charade of a marriage or get some help in resolving the issues that have you sleeping in different rooms. As long as things continue as they are, it really does not matter if she is cheating on you or not. (Not sure if it is really cheating if both parties have checked out of the relationship as you seem to indicate.)

Well, if she is (cheating) then she shows evidence of being interested in sex.

You two sleep in separate bedrooms and there's been no sex?

When and why did this start?

yes this is a sighn she is cheating

No and maybe. When I started working out and losing weight. I felt better about myself I started dressing sexier too. I was in a sexless marriage too but I wasn't cheating. It just made me feel better. I was 4 6 at the time, age does not matter. However as other have pointed out it could be but it's not a positive yes answer for that you need to talk to her. The real question is if you're living in separate rooms and not having sex do you still have a no sex with anyone else commitment? You need to discuss that with her. Marriage is a legal piece of paper binding you financially but not sexually. That part is between the two of you to decide and you should get a clear answer from her on that.