I don’t know if I truly love him

Hi!

I suffered from social phobia (since my early adolescence), and so I began dating late – at about 21. After meeting several guys (mainly online – and then in person), I finally met this guy whom I liked and with whom I felt comfortable. We began going out frequently, and then we began a relationship. It’s been 3 years now, and he has been the only man I’ve been intimate with.
The thing is... After all this time, I don’t know if I truly love him. I really like him – he’s beautiful, sweet, present, understanding; we do a lot of stuff together that we both appreciate; our relationship is based in good communication; etc, etc. And I can be quite jealous about him. But I’ve never felt ‘passion’ for him. What I feel is tenderness, closeness, respect. And sex is ok/good, but never fantastic, even though we both try to ‘our best’. He seems to appreciate it far more than I do.
The consequence of this is that, sometimes, I feel that, deep down, I’m still searching for my ‘soul mate’/’enchanted prince’ or whatever. I’ve had phases in which I’ve spent hours on the internet talking to random guys, or to old male friends, several times clearly flirting or engaging in sexual conversations. After that, I always felt terrible, and so I managed to control myself, and now I don’t do it. Also, frequently having to spend a lot of time with guys my age, at work, I often found myself ‘lusting’ over them, and having sexual dreams with them.
The problem is, this being my only experience with a man, I cannot compare. What is a loving relationship like? Do I love him? Am I naively expecting too much of a relationship? Can sex be naturally better? Sometimes I have the desire to cheat on him, and experiment sex with another man. But I know I wouldn’t do it.
I’ve been in love before, and it was much more intense than whatever it is I feel for my boyfriend. But those were almost platonic and ‘at distance’ feelings, without a real and close connection. So I have no idea how I would feel in a relationship with one of those guys I thought I was in love with.
Somewhere along our relationship, and consumed with doubts, I asked for a break. A time to think things through... He was devastated. And I felt terrible for making him feel that way. Also, I felt like I was voluntarily cutting my own leg without any good reason. We ended back together.
But there’s always this doubt... We don’t live together yet (because it is not economically viable yet), and I don’t dream about it, nor do I fantasize with a future together...
Am I clearly not in love?