<human>: Can you condense the text into a few key points?

I have been with my boyfriend for 4 years, I met him just after I split up with my ex girlfriend (8 month on/off relationship). I fell in love with my boyfriend instantly and we moved in together after only a few months.

My current LTR was a slow burn kind of love. I wasn't infatuated with my boyfriend, and my love for him was a deep attachment that basically started from day one. We were so compatible and comfortable that we traveled for a whole year together without issues.

In comparison my relationship with my ex was exciting, tumultuous, painful and very romantic. I was heavily infatuated with her. There was very powerful lust in our relationship that had us tearing at each other's clothes one minute, then having a yelling 'break up' match the next. Looking back, I was definitely in love, if not also a little crazy.

Which brings us to now: I have always thought/dreamt about my ex from time to time throughout my relationship with my current partner. But usually it was not obsessive. Recently, however, I have been thinking about her solidly for a month or so. I find myself reliving memories in my head a lot, and missing the feelings we used to share. These feelings of lust, romance, excitement, drama etc are missing from my LTR. I keep asking myself if this missing her means something. 

Slight background on me: I am bisexual, but homoromantic. I am deeply attached to my partner and want him in my life forever. I have been honest about my homoromanticism with him, and we are open minded to opening our relationship in the future. So I am not asking for advice from the 'to break up or not break up' perspective. Rather... is it normal to still think about an ex after years of being apart? Why is this happening?
<bot>: I met my current partner [26M] after splitting with my ex [25F] - it's been 4 yrs and now; suddenly I keep reminiscing/thinking about her and it's stressing me out.