Judging from your post your insecurity and depression are making judgement on this situation clouded. You're afraid to come off as "insecure" for wanting to express how you feel. Ironically, the fear of how you are perceived by your BF is actually more insecure than standing up for yourself and your feelings.

You should express how this is making you feel. I don't think there's anything wrong with feeling the way you do. It sounds a little excessive from him to be spending so much time with her rather than wanting to spend that time with you. Not saying he's supposed to spend every waking moment texting/alone with you (and neither should you) but I hope you get my point. Men and women can totally be friends but there's a thin line when it borderline just becomes emotional cheating.