Is this my problem?

15 months ago I broke up with my bf of three years, because I thought I fell in love with someboday else. I broke his heart, and I felt shame and guilt till this day.

At the time, it felt like there were many reasons that made me leave him, e.g. I felt pressured about marriage (he suggested to think about wedding, since we were engaged), I felt abandoned (I just moved to a new city for him, but he was not around for the first 2~3 weeks), there happend to be this new person in my life with whom I hit it off really well.

I tried to move on with my life with the new bf. Recently, we started talking about buying an apartment together. then I started having the thought of leaving him. I started thinking about all the parts I don't like about him (he is a bit aloof and have somewhat a negative energy) and if I can live with it for the next couple of years, and questioning if i really want to make the commitment of buying an apartment with him. I constantly thinking about telling him we should break up, then thought of his sad face, I couldn't bring myself to do it.

Then I remember I experienced similar feelings with the previous boyfriend, when I felt I was going to marry my him and spend my ENTIRE life with him, I left him for someone new.

I've been a responsible person my entirely life, good university, grad school, a good job. I never thought of myself as iresponsible or afraid of commitment. But maybe I am, if this is my problem, I will work on it, but if the current bf really isn't good for me, I should bring myself to end it.

Thanks you all for reading.