How do I get over the feeling that I need to choose between my two partners?
I have been with my primary for 4 years, and we have been in a long distance relationship from the start - I live in the US and he lives in the UK, so we skype every day and spend 4-6 months apart at a time. We were each others first boyfriend/girlfriend and first sexual partners, and we were monogamous for the first 3 years of our relationship.
Things changed this year (my last year of college) when I began to realize that I missed out on dating and exploring different people. I love my boyfriend and figured it was just one of those things I would wonder about from time to time, but when I told my boyfriend this he encouraged me to experiment with other people. 5 months later and after a tentative start, I am now also in a relationship with a fantastic friend at my college. My boyfriend doesn't have a jealous bone in his body and is still very happy with our relationship, and my new partner is also very happy with and open about the situation.
So everything seems pretty perfect, but for some reason I can't get over the feeling that I need to choose between them. Being with my new partner has made me realize that he understands me in many ways my boyfriend doesn't (my new partner is essentially a male version of me to the extent that we think of each other as brain twins, whereas my boyfriend comes from a very different mind set and we have had to spend a lot of time trying to understand each others perspectives), and it makes me look at my relationship with my boyfriend a bit more critically. There have always been cultural differences and a 6 year age difference between us, but now they stick out to me more than they used to. I have also been spending a lot of time with my new partner while my boyfriend has been busy with family events, so as I grow closer to my new partner I worry that I might be drifting apart from my boyfriend.
The most noticeable difference is that before the open relationship I was happily thinking about marriage and children with my boyfriend (he is at the age where all his friends are getting married), but now suddenly I am realizing how young I am, and the idea of being tied down is suddenly repulsive. I think I still do want those things with him eventually, but not for a good long time (It might also have something to do with his tight-knit, traditional English family, who make me feel smothered). I'm left feeling confused, I thought I had it all planned out before.
In a nutshell, being with my new partner is making me wonder if my boyfriend is as good a fit for me as I used to think he was. I keep wondering if I'm supposed to break up with my boyfriend because I've found a guy who gets me a lot more than he does, but I suspect that's my ingrained monogamous mindset coming through. Am I overreacting by wondering whether we should still be together? How do I get over this mono-mindset? Has anyone else experienced feelings like this towards a partner? Any advice would be appreciated!
p.s. thank you in advance for your help :3