I don't understand why I'm unhappy

My boyfriend and I have been seeing each other for about half a year. Facts alone, things are great. He treats me well. He's emotionally available and expresses his feelings for me. There's little to no drama. He introduces me to family and friends. We've moved into the comfortable phase fairly quickly....and I think maybe he's moved on to the struggle of keeping his own life/self identity (ie before he'd skip or cancel some of his extracurriculars to spend time with me but not anymore after we talked about the importance of having your own life outside the rel).
And I'm trying to keep my life fulfilling without him too but I'm starting to feel bored or dissatisfied with our time together. I enjoy our time together but sometimes leave feeling like I want more or we could have done more. Maybe we stay in too much. Maybe he dominates convos. Maybe he's slacking in effort for our dates.

He's a great guy...really sweet and loving...been there for me and encourages me...he's what I thought I always wanted. And I still want to be with him and only him. So what's the deal with me feeling down? I am very new to the long term dating world (used to have flings and "friends"). So am I just not used to the stability and predictability (no rollercoaster and drama)? Is it just a relationship phase? Is it incompatiblility? Am I being selfish/high maintenance in the attention dept? Is it just stuff that can/need to be talked out?

At first glance, I'd just say the rush of a new relationship is wearing off. The excitement tends to have low and high periods, but you can always come back to each other after focusing on your own life for awhile or discover new things about each other over time. There's a comfort and a tenderness in close, long-term relationships that makes up for it.

Personal opinion, anyway. I guess it depends on whether or not it's the excitement and intensity in particular or something else. Maybe you could find something new to do together.

I agree with Tealeaf said, just felt like say something more. Inputting other things; things happy like this. When you first date everything is exciting ad than after awhile I guess everything seems so new and great to you. Overtime when you keep doing the same thing over and over the exciting tends to wears off so try finding new things. Play boardgames together, go out and tell him that it's okay if he wants to hang out with his friends. Speak to him and let him know you're feelings but let him know that you still love him. Don't let him believe that it's a bad thing cause every relationship goes through this and ends up feeling like it's over when it's in fact normal.

This actually happened to me as well, I expected my boyfriend to pay attention and I realized how selfish that would be. Now I want to learn how to do new things. There's still arts and crafts things I want to learn to do. People grow and learn everyday, if we stayed the same I strongly believe we'd be boring. Used to fear change; now I actually get excited for change and look forward to new things in my life. Try new things together, talk about new things together, there's so much to talk about. Watch TV shows together that you might find interesting. Hope new things comes to you're relationship. <3 Wish you the best!