Bpd and boyfriends/partners

I am having a real hard time at the moment, and it goes for a lot of things in my life. There really isn’t too much that sets off my bpd as intensely as my partner - we broke up 9 months ago and have recently gotten back together, we have admitted it’s probably us for the rest of our lives, We do know we love each other endlessly. But there is so much pain in my chest when I think/ or we talk about the people he’s been with during those nine months. I let my bpd get the better of us earlier in our relationship (was one of the main reasons he decided to end it), and I really don’t want it to now. I let it get the better of me earlier and I went through his photos on his phone and saw some things from the nine months I really didn’t want to, and now I’m all tingly and angry and I can’t even communicate how I feel. I know I shouldn’t be going through his things, That’s a given. But I shouldn’t be feeling this horrid and gross and angry. It’s so hard to pull out of these feelings and I don’t know whether I’m in the right or wrong for being upset about seeing those things.
He’s really understanding with my bpd (and I’d never take that for granted now) but sometimes I feel I don’t get the reaction I want/need for my emotions and I can’t stop that, even if I know it shouldn’t be given to me.