Exceptions to the signs?

So I've been going out with a pretty odd Sag boy. I hear they are known for not able to commit to anything. Being a cancer, that can be a problem since we are like, COMMIT TO ME! MARRY ME!!! and all that jazz. I know because I've been talking about marriage since month 2. I have Cancer in my Venus as well as my Sun and Mercury so I'm a pretty strong emotional being and can't deal with short term relationships. (we've been going for 2.7 years)

Before we started going out, I did check the horoscopes on how to deal with him to make him happy. I had the intent to get him wrapped around my finger. Somewhat control and not want to leave me. Why? cause I'm female and I'm insecure LOL. I thought this would be a challenge because of him being a Sag. He was the first Sag I've dealt with as I had a long string of Gemini boys (each as bi polar and neurotic as the next) and one Aquarius (Was selfish and wanted my attention ALL the time and fought with ALL the time). (most of my relationships last for a year or two)

I started with caution, not sure if he was going to do anything against me. I couldn't figure him out and yet he was too good to be true. When I first met him, both away from home, hundreds of miles away, he was really really quiet. Almost Unemotional and he always had this furrow look that intimidated the weak heart-ed. Getting to know him, he's pretty crazy and spontaneous as I was. I mean, I'm very good at distracting people 😆. He would tell stories of the dumb shit he use to do when he was a child like running into walls and how popular he was until he became isolated in private middle school.

Though what puzzles me is the commitment bit. In the years that we've been together, He's done absolutely nothing wrong! Am I just pessimistic and bitter about all my last guys? Comparing to him and realize he's the best thing since sliced bread— I'm his technical first girl, I took his virginity and hell, I taught him about swinging and I tried to test him out and see his reaction to other girls. Both girls, he could not get the means to screw either. I was flattered that he could only get it up for me but my attempt to flesh out any hidden characteristics have failed o.o. I mean I seriously landed THE ABSOLUTE PERFECT GUY. I'm ecstatic and finally feel like I can let myself go and become just as obsessed as he is to me.
Perhaps I do this because I don't trust myself? He's Sag rising, Sag sun, cancer moon, sag mer, scorpio venus, pisces mars

to further my point, He's super romantic. I mean he never misses the chance to open the car door for me, I gave up on paying for myself because he's quick at getting his wallet out first, He loves taking me out on dates, he's a beast in bed, He's taken me to Rome, he took me ballroom dancing and we've explored our relationship in ways that many our age are too immature to do together. We love co-op games that require a lot of communication and challenge each other in some games. He loves the fire I have behind me and I love his cool nature, quick wit and reliability. He makes my heart flutter with random text messages of poetry. I can't resist him. I can't. but why do I hold myself to do so? What's holding me back—