While it’s true all mimikyu are envious of pikachu, how they express that varies from mimikyu to mimikyu. Some are at odds with pikachu and display violent behavior in the vicinity of one (even going so far as to engage in intense battle with them on sight), but others may prefer to watch pikachu from afar or shyly befriend them in order to understand them. It’s very much like human jealousy, really. Some people befriend the people they envy or respect, and others spend much of their lives allowing their jealousy to fester into toxicity. Naturally, the latter isn’t exactly the best outlook for one’s psyche, and as such, it may be prudent to help your mimikyu find a healthy way to manage their frustration should you find yourself training a mimikyu of the more violent, negative variety, but if you find yourself training a mimikyu of the positive variety, you may be pleasantly surprised that it will do perfectly well around a pikachu teammate.

In other words, what you’re describing sounds perfectly normal, anonymous. Your mimikyu is evidently the type that deals with their envy by building understanding. It’s good to hear that your mimikyu gets along so well with your raichu! May their relationship only strengthen from here onwards.