My team would benefit having a fighting type pokemon, but my male kirlia decided he does not want to evolve so my only other option would be to catch a new pokemon, basically replacing him. How could I do this without upsetting him, as I wouldnt be able to fit him on the team anymore?

Before anything else, have you considered a compromise—perhaps teaching fighting-type moves to your other pokémon or using a combination of elements to cover the same types that a fighting-type would normally handle? For example, although kirlia may be weak to the steel-types a fighter can handle, many trainers teach theirs Focus Blast to counter this exact problem.

If you can’t avoid replacing your kirlia, you may want to consider keeping him as a companion pokémon. These are pokémon you keep around your home, pokémon who don’t count towards your six-pokémon limit but typically can’t accompany you on your journey. If you’re a trainer who doesn’t normally wander far from home, this may be perfect for you, as it will allow you to continue keeping your kirlia in your life while still enabling you to create a fully balanced team for battling.

Alternatively, if you do travel far from home, be sure to leave your kirlia in the care of someone he can trust as well. Call as often as you can while on your journey and maintain your bond as much as possible through conversations over the video phone. Visit your kirlia as often as you can as well.

Up until you leave, however, be sure to bond with him and make it clear you still value him, of course. Spend time with him. Explain to him what it is you need. As a psychic pokémon—especially one with a specialty in emotions—your kirlia is in a far better position to understand what you have to say than most others, not only because of his natural intelligence but also his ability to sense that you’re genuine in your feelings.

But it’s important to leave him somewhere you’ll be sure to return to, especially your family. I’ve heard of trainers promising to return for released pokémon far too often, only to forget later on, and it really is devastating to the pokémon involved. By leaving him with your family or a trusted friend, you’re saying to him that returning for him will be a guarantee and that contact during your travels is promised. It really is little things like these that will make the transition easier, but it’s important to be as gentle but as honest as you can be with him—and that the sooner you tell him, the better.