<human>: Can you give me the gist of the text in a nutshell?

First of all I know we're young, but we've been going out for 3+ years. We don't live together.

She left her snapchat account logged in on my phone and I saw a long list of snapchats to and from this one guy from her work who is 20, and there were a lot.. The snapchats also go on until about 2:30 am most nights, even on nights where she's said goodnight to me and told me that she's going to bed at around 1:00am.

I'm suspicious because a couple of days ago she snatched her phone away from me when I picked it up and was really defensive with it, even though I wasn't even using it. She also acted really defensively when I subtly mentioned that I didn't recognise the username of her top friend on snapchat (who she sends the most pictures to) which is the guy from work.

I really don't want to come across as jealous, but should I talk to her? I'm hesitant because something similar happened a year ago and I brought it up only to be told that I was being overly protective and jealous. To be honest this time around the situation is really suspect and I just want an outside opinion.
<bot>: I [19M] found that my gf [19F] has been snapchatting a male colleague a lot and has been acting defensively.