<human>: Can you condense the text into three sentences or less?

So I went on a study abroad semester last year and I returned recently to find out that my girlfriend has been getting closer and closer with a female friend of her's, to the point that they may want to go out. 

We were never in a fully monogamous relationship, and especially while I was overseas, we toyed with the idea of an open relationship. She also told me that she had a crush on her while I was away, so this really isn't that surprising. 

While I'm very much open to the idea of polyamory, I can't stop feeling envious of the time they spend together since they're still in that honeymoon period where they chat till late at night and go out a lot, whereas obviously things between me and my girlfriend have died down a bit since it feels like we've exhausted the novelty of having each other. 

What can I do to manage these feelings of envy, and do you have any advice for a first-timer in a polyamorous relationship?
<bot>: entering into polyamorous relationship, envious of their honeymoon period - advice sought for that and polyamorous relationships in general