Is is disrespectful to wear military surplus gear without having served in the army?

Michael,

These clothes are a dime-a-dozen, with or without any insignia. They're sold at military surplus stores everywhere.

As far as being "disrespectful." There will always be someone who has something to say about what you do, believe, utter, etc. You can't please everyone, but you should not even try. You know your own motivations. Be your own person. Bending to the whims of everyone is not only foolhardy, it's impractical.

You might have heard of the term "stolen valor." You should know that there is no such thing as "stolen valor." None. It does not exist. It only exists in the minds of people who want special treatment, which is (unfortunately) all too common today.

Laws against fraud already existed, so the Stolen Valor Act mostly duplicated existing law, and hence, was unnecessary and wasted resources. It's expensive to write a law because of the time spent by legislators, lawyers, etc. The law being litigated by courts also a huge waste of tax dollars.

This was all precipitated by people who think they are so special that a special law against fraud has to be created particularly for them. Pandering politicians step all over one another trying to appease these special snowflakes, mostly to be popular and win re-election.

I wouldn't say it's disrespectful. Military gear is very well-designed and sturdy, and you paid for it with your taxes. It's disrespectful to wear medals you didn't earn, or badges of rank you don't hold. The clothes themselves are just clothes.

you have to be dating another military man

Yes.