Feelings for someone in a relationship
I've known this person for about a year now and we seem to have a lot of compatibility and chemistry. I'll admit, when I first met them, I did feel an attraction, but by no means thought it would turn into feelings being developed. After getting to know them a bit more, I discovered we share a lot of the same values, same interests and similar desires in life. I genuinely like them as a friend and they have helped me build a lot of confidence and just an all round warm person to be around. Of course, I'm in no place to tell them how I feel, because they are in a relationship. I'm in no hurry to enter a relationship right now, as I am happy being single, so it's not a matter of feeling lonely. It is just a genuine connection. I guess I just want to know if anyone else has been in this situation and if there's any advice on how to keep my feelings at bay.
I'm both sorry and happy to hear about the situation you find yourself in– it seems like it is bittersweet, with the exciting potential of a new relationship (of whatever form it takes), and the melancholy that comes with seeing that person be with someone else.
I think it's important to remember that it's okay to feel more than one conflicting thing at a time. You can be happy for them and jealous; enjoy being their platonic friend and still want more. You don't have to commit fully to one or the other, and I think you are better off just being honest with yourself about your feelings and doing your best to adapt as circumstances may change.
As I'm sure you know, unfortunately people break up all the time, and people we once thought were unavailable to us in a particular way suddenly become potential partners. It is both okay and possible to 1) want the best for this person in their relationship, 2) befriend their partner as well and have a new genuine friendship, 3) yearn romantically for this person, and 4) secretly wish that they were with you instead, all at the same time!
I think it shows a real emotional maturity to identify having chemistry, a genuine connection with someone, and acknowledge that you're happy with where you are in life and don't need to put a name to it quite yet. Finding the kind of connection you describe with anyone is a special and rare thing, no matter what does or doesn't come of it. Whatever the capacity, I hope you and this other person are able to be in each other's lives for as long as you care to.
All this to say: you don't need to keep your feelings at bay. It's possible to feel things fully, deeply, and honestly, while making sure keeping your behavior (i.e. how you act on those feelings) in check. If in the future you find your feelings growing more intense such that you're not able to continue being this person's friend, I think that is a separate consideration that we here at the forums will always be happy to help you talk and think through.