Time to move on, or should I let it play out a but longer?

I’ve (31M) been in a relationship(28F) for a few months. Things originally started off well, like most early relationships do, but I’ve started to lose feeling seemingly out of nowhere.

She’s a really sweet girl, I find her attractive, we get along, and have similar interests. The problem is that I think my emotional connection with her seems to not be progressing, possibly even regressing. I don’t know if I ever could see myself loving her and the passion has died much faster than I’m accustomed to.

I’ve been in several long term relationships where things almost got to the point of marriage, but in the end we always had some large falling out due to some reason or another.
My last relationship was only about a year and a half long, but actually ended on good terms. I’m seemingly still stuck on that relationship also (not a first).

The combination of factors makes me think it isn’t best to stay in this relationship. If it were right for me, I wouldnt feel so conflicted.
On the other hand, I’m worried I may be making a major decision too quickly and that I might need to give things more time.

I’m not sure if I’ve just raised my standards to some unreachable point after my previous relationships (every relationship progresses differently), or if I’m making the right decision. I really care about her and don’t want to hurt her, but I also think she deserves to be with someone who will be able to love her. I don’t think that’s me. It seems that in my past experiences the time for me to move on was obvious. Now, not so much. Thoughts?

TL;DR I’m in a fairly new relationship and I’m losing interest. I’m not sure if leaving is the right decision because it’s usually obvious.