I feel for both you and your partner. I've been on both sides of the equation with this. When my partner started taking this super seriously 2 years ago, getting a trainer etc, I supported him by offering to help split the cost with the trainer, helping with supplements, equipment, clothes etc. But as time went on, I felt slightly taken for granted with it, not because I wasn't getting anything personally out of it, or that he expected me to help, but more because of how deep he got into everything. It almost felt like I was an outsider, to the point of almost being an afterthought to the whole thing between him and his trainer, and it started bringing out my insecurities in my own physique and personality. Like I wasn't really needed unless I could provide some sort of assistence.
What you two need to do is talk, communicate, and listen to each other. Find ways to support one another, but also encourage each others endevors. He should be encouraging of your ambition for your body transformation, but you should also work to keep the connection open with his interests as well.
People can get completely obsorbed and lost in the lifting and bodybuilding lifestyle, both of you should do your best to keep those connections open so that no matter what, you'll know you're there for one another. Make time for one another, even if its spontaneous, to show that no matter how much you change physically, that you're still the same people you were before all of this. I'm currently working on that myself, and as a result taking all this a lot more seriously to overcome my fear and insecurity of not being adequit and not wanting to feel or be left behind. It's a struggle, but both sides need to keep pushing one another and be supportive. If one side is doing all of the supporting and the other is doing all the taking and taking things for granted, it won't work in the long run.