Trust or Not Trust?

How do you discern trust? This topic seems to be an issue for many people, including me. I have trusted in the past and was betrayed. I learned a great deal about the dark side of life, people, psychology, and myself.
I learned to trust myself, because each time I felt suspicious I always tried to talk myself out of it. I would rationalize the incident in such a way that it was OK. Or, I could say to myself, "I will trust him." The effort usually didn't last long. I confronted the boyfriend, argued about it, stayed in the relationship, and eventually broke up as I eventually found out the truth.
In a new relationship for about 2 years now. He seems very devoted to me. He takes care of me, is polite, spends most of his time with me. Says he loves me and so forth. I have no complaints in this area.
However, his female friend has become an issue for me. We spoke about it once about year and a half ago. He asked me to trust him, assured me of his love for me and so forth. I have been going along with it.
I think I am a little slow to interpret and see reality. But this is what I see since we had out conversation a year and a half ago:
I see that when he goes out with his male friends he is very transparent with me about it. He tells me ahead of time. Occasionally he sends me pictures of the group. Afterwards he talks very openly about the event. I appreciate that very much.

With his female friend, howver, I'm seeing something different. They work together, by the way, on a community organization. Last year he went out of town for this organization. He spend the night, came home the next day. Said he was driving with a group of guys. After he returned home, he posted pictures on FB. I then saw that his female friend was there as well. She's is part of the organization making her presence legitament. However, my boyfriend did not tell me ahead of time she was going. Afterwards he did say, "Oh did you see the FB pictures?" I said, "Yes." Then he said, "Oh, So & So was there. I responded with, "Yes I saw that." There was no further disucssion about it. About two months later he mentioned that he and her drove out of town together in his car because the guys all canceled and it was cost effective to drive together. Months later I asked if he and his female friend also shared a hotel room because it, too was cost effective. He said No.

Over the next several months I noticed this recurring pattern: with guys he's open with me, she, he is not. He incidentally mentioned that he was at her home helping her with kitchen cabinets of some sort. Although it was a quick statment with no explanation. I let it go. There have been other incidences as well, but not at her home.

Recently, all of us were together for a holiday dinner. I get home and my boyfriend hands me a gift for me, from her. A few days later, I see an opened gift on his dresser. He said to me, "Did you see that gift on my dresser, that framed picture of us? That was from" . . . his female friend.

I felt very un-nerved by her gift giving method that did not include me on the actual exchange. Why would she do that? We sat together for several hours at dinner. She never once mentioned she gave us gifts via my my boyfriend. I thought that if she mentally embraced us as a couple she would have said something to me along the lines of, "Hey I have a gift for you two. . ." and so forth. But she didn't. Apparently there gift exchange was private between them at some time or anothr. I don't recall seeing her walk in to the dinner with gifts to hand out.

Recently, I checked my boyfriends phone and read their text messages. There is nothing romantic, or sexual. Most of the dialogue is bussiness, a lot of family conversations, some personal encouragement type of comments, some of him helping her, and asking her if she needs anything, him sending her pictures of himself sitting outside alone at his fire pit, and her sending him picures of herself with her personal interests.

At that dinner I mentioned, a man was standing right next to my boyfriend's ear. He verbalized a very flattering comment to my boyfriend about how nice his female friend looked. My boyfriend did not respond. He made no effort to respond or even acknowledge that he heard the comment. Although, I heard it and I was sitting two chairs over. I read in my boyfriends text to her, that she looked great. And about this gift that she gave him to give to me, he and I never talked about it. Although, he texted to her that I liked it. Why would he tell her I liked it, when we never talked about it?
WTF? I'm getting uncomfortable with all of these little nuances. Do I trust my gut? Or is my gut blowing things out of proportion damaged from previous experiences? Do I trust him? Should I talke to him about it, or let it go?
I feel that I want to wait a little while, becaue she might be moving away, anyway. But either I trust him, or I trust my gut.