Confused and torn about love. Wracked with self doubt.

I've been in a relationship with my partner for over 3 years now. We have been through a lot together in that time - (The feeling of) falling in love at university, moving from place to place, coming out about my porn addiction and committing myself to being honest and clean. I've abstained from porn for 10 months now, but I'm still, you could say, within the range of time it may take to recover.

The problem I am having is this: I'm not certain about if I still love my partner, or if I ever really did love her. For all that I know it could just be an elaborate lie that I told myself and her, despite that when I admitted my love for her it did at that time feel right and as authentic as I had ever experienced. I know this much: I care about her very much, want her to be happy, would love to be the one that can be a source of happiness for her rather than pain, I would die in her place. But even still my brain rationalizes this: couldn't someone who just cares about someone very much feel this way? Does it really mean that you love someone? I don't get that feeling people are said to get with someone they love (if I did in the beginning I don't now), in fact, I often don't feel very much of anything at all. In moments where I am smiling with her and know I should feel happy I become aware of my innermost self, and that doesn't feel happy, it feels in pain and like something is wrong. Maybe it's just my depression, or does that make me unloving, or worse, incapable of love and happiness?

I am torn in knots by self-doubt with this, my thoughts often try and persuade me that what we have is a great friendship, that it's time to move on and let her go, that I am not the one she is supposed to be with. Someone else will be more suited to her and make her happy. I have so much to hold on to, but I simultaneously can't bear to be selfish with her when out there could be the relationship she deserves. If I really don't love her, I'd have to let her go.

We have talked about this together, and I know it causes her a lot of pain to see me question my love for her. She says that the way I am with her and what I feel for her, which is like I care for her in a way that feels unique to her, that I couldn't have with another person - she says that she believes that to be love and that whatever my capacity for love is, that's good enough for her but I just don't know. I don't want to cause her any more pain but she says how love hurts but is worth it. I agree with her, but there surely has to be a point where it's too much.

In a way, my mind feels like it is trying to move on. I started talking to someone online with the intention to just make a friend and we have connected well at this point. However, despite my innocent intentions, my brain remembers how I used to long-distance people growing up, and the thrill of getting to know someone new. At times I feel like it is trying to turn my friendship into something I don't want it to be, more of a getting to know someone romantic fantasy. I hardly know this person in reality, and I intend to stay committed to my partner so long as I stay with her. It's just how these thoughts make me feel that hurts, as they go against what I really want.

What are your thoughts about my situation? Feel free to share below, I'm truly at a loss.