Sorry, did I read that right? You agreed to this major change last week and she's been out with someone (at least) three times in that time? Did you mean to type week? You say that you slowly started having feelings of jealousy. How does slowly apply in a week? Could you please clarify before I attempt to give any other insight?
I see that you hurt, but I don't totally understand the timeline. Would you please be willing to clarify?
Are you saying and you and your partner dated for 3 years, and last week you decided to open the relationship?
And your partner is now dating and spending the night with this new lady from her team, on top of team practice 3x a week, and seeing Lady there, because Lady is also on the team?
And you have had to see Lady lots also, even before they started dating?
You are coping by staying with a friend this week?
When do you and partner have your own regular dates?
Even though I'm not entirely sure on that timeline, I think you could ask partner to pause dating any NEW people. This is tough enough with dating Lady. No dating even more new people on top of that.
Determine if you still want to live with your partner or not, and if you want polyamory or not. I don't know if you and partner would be willing to see a poly counselor.
Even if you want polyamory, you might not be compatible for doing polyamory with THIS partner, if this is their poly practice. This sounds like poly hell to the max if your partner is going at it kind of recklessly, or like a kid in a candy store. What's the big rush?
COMMON PITFALLS IN OPEN RELATIONSHIPS Many people who are in a primary relationship stumble into an outside relationship either by choice or by chance, and once involved, things can go beautifully or can go terribly awry. Here are some of the most common problems that develop and some ideas for
I don't blame you for feeling jealous, that is a lot to deal with all at once. Your partner should not be harming your mental health like this. Tell her you need her to break up with the girl from her sports team.