Help! Partner wants to open relationship after falling in love with a friend
Any advice is welcome.
My partner wants to open up our relationship after being monogamous for 2 years. When we started dating my partner mentioned that she was polyamorus but would be happy with just being with me but that if she did start catching feelings for someone then we would cross that bridge when we got to it. I was under the impression that we were perfectly happy with just the two of us, though we had discussed having sexual experiences with other people at some point (which I'm perfectly fine with as long as it's both of us participating in some way). Now she is wanting to open up our relationship after developing romantic feelings and connecting on a deep emotional level with one of our friends (I'll call this person Aspen).
We first met Aspen and their friend, Rue, at a bar on New Year's Eve 5 months ago. We grew close very quickly and went to parties together, had movie nights, etc. Last month Aspen's mom got diagnosed with stage 4 cancer and also their dog had to be put down suddenly. My partner had the most free time in our friend group so she was able to spend the most time with Aspen to keep them company and make sure they were doing ok. Aspen and Rue are best friends, Aspen is in love with Rue but Rue only likes them as a friend. Almost a week ago my partner and I have sex with Rue. It was rather spontaneous and impulsive, which I regret now (I was the one who initiated). The next morning Rue tells Aspen about it. Aspen is very upset and cries. My partner is also very upset about the possibility of losing Aspen's friendship over it. Rue and Aspen talk and work it out. My partner goes over and talks with Aspen and works things out with them as well. As for me, I had been rather distant with everyone for the last 2 weeks because I was finishing up all of my final exams at my university and working 11 hour shifts for three days straight. So I was just starting to talk to everyone about the situation 2 days ago.
That is when my partner tells me that she is in love with Aspen and wants to open up the relationship. I'm blindsided and feel betrayed because I had trusted my partner would be able to be loyal to me. Now, after talking about it, we are stuck. I have thought about the possibility of being poly with my partner because she is and I want her to be happy. But I just can't bring myself to be ok with her being in a romantic relationship with someone else. I know I would be resentful of the other person and grow jealous. It's just not me to be open to that. My partner wants me to be ok with her ability to love other people equally. I realize that makes us incompatible. Which is why we are giving ourselves the weekend to think about where are relationship is going to go from here. Because one of us will have to compromise or we will have to breakup. I love her so so much and I can't imagine having to leave her. We both don't want to breakup but I don't know what to do.