SUBREDDIT: r/relationships
TITLE: When is it not time to "fight" for someone?
POST: I will try to explain as best I can. I am a 26 male and she is a 23 female.

We have been playing around together for a while now, bene-friends if you will.  Everything has been going smoothly for the past 3 months now. We have known each other for about 2 years now, only in the past 3 months have we been sleeping together.

That is to say until a new guy came along in her office, they started hanging out more and we started hanging out less. Though we kept the same arrangement, they have not slept together but have gone out on dates.

I am sitting here wondering if I should say something, tell her that I had started to develop something in my mind that is more than just what we are now.
TL;DR: 
'Friend' is starting to date another guy while still sleeping with me, I want to tell her how I feel. Should I?