Generally speaking, gallade tend to be rather protective of their trainers, some more than others. So I wouldn’t say that the people you date are latently evil, @hoshikostar. It may be more that your gallade is finding it difficult to trust new people you bring into your life, especially if it’s been just the two of you for a very long time.

My advice would be to try and acclimate your gallade to a new partner the same way you would a new pokémon. Do it gradually and in comfortable settings, and make it clear to your gallade that your partner means him (or you) no harm.

If he continues to express aggression towards your partners, it may also be jealousy or a genuine fear of something he’s detecting. If it’s the former, have your new partner interact with your gallade in mediated settings to establish their intent on forming a partnership or family with him as well. (In other words, have your partner reassure your gallade that they have every intent on including him in activities, rather than excluding him and monopolizing your time.) If it’s the latter, reassure your gallade that you trust his judgment, but let him know that you can’t act on his advice unless he opens up to you.

Finally, consider training alongside him, rather than simply guide him through exercises as a trainer usually would. In doing this, you’ll remind your gallade that you’re not simply someone who needs constant protection but rather an equal, and thus, this should reassure your gallade enough to be a little less overprotective.

Best of luck!