Me [21 M] with my wife [21 F] 3 years, I think she cheated on me last night.

I'm not doing great right now so I will just jump right in.
I've been with my wife for roughly 6 years, married for 3 of those. She has always been the type I would describe as "fiercely loyal." Which is why I'm having such a hard time coming to terms with what I believe is happening.
Whether she cheated on me or not, I've known something was up for a few weeks. I know her better than anybody and I'm very good at reading people in general. I pick up on slight personality changes very easily. Onto the story:
It started a few weeks ago when she started hanging out with one of my best friends [21 M] (We can call him Mark). We live in the same apartment complex with him and his wife [22 F]. When they would meet up, it would typically just be the two of them over at his apartment. I know some people aren't comfortable with letting their SO be alone with members of the opposite sex, (or at least where I'm from) but I honestly didn't mind because like I said fiercely loyal and I didn't feel like I ever had anything to worry about.
The first thing that tipped me off was when she started getting secretive. I started noticing she was always texting someone, which in and of itself isn't out of the ordinary because she makes at-home appointments with her clients. But what tipped me off was her body language while she was texting: very reserved and almost always facing towards me so I couldn't see the phone.
To preface this next part, her iPad is linked with her iPhone so everything she gets shows up on both, including texts. Now I want to say I have never snooped and I don't agree with it. I think constant snooping with no reason other than paranoia is bad for a relationship in the long run. But I noticed some texts coming from Mark and they were definitely not things appropriate between two married people. But this alone isn't enough to convince me anything happened. They weren't sexting per say, just talking about sexual topics. (If it will help, I can go into more detail about this.)
At this point I think she realized I was onto her (whatever it is she's up to), because that's when all texts from him stopped. But I knew they were still in contact because she would still tell me of conversations they had while not together. I found out they have been using snap chat's chatting feature to talk. And I have no way of knowing what they are talking about or anything because snap chat deletes everything after you read it (I think. I don't really know how snap chat works other than sending pictures and chatting, and even then, I rarely use it).
Ok so all of this has been happening but I still didn't think anything happened between them. I trusted her and yeah maybe some of it was inappropriate, but we have a very open relationship and are extremely honest with each other. I figured if anything would have happened that would give me cause to worry, she would have told me. And then yesterday happened. We both worked until 8 last night and then after she got off work she headed over to Mark's place.
Note: She has a good alibi, I've seen texts from Mark's wife inviting her over. So I know that his wife was, at the very least, in the apartment when she went over.
Now at this point I have given up on my no-snooping rule because something is definitely up. So I started going through everything I could last night to try and figure this out. I ended up going through our google account history and that's when I saw it.
A bunch of google searches basically saying:
"bleeding after being fingered"
I DIDN'T ****ING FINGER HER LAST NIGHT. We haven't had sex in weeks. Mostly because we really are both busy people but even when I tried to initiate over the last week she kinda just blew me off.
This morning I checked the history again and there were more searches about it "i got fingered last night and got scratched and its still bleeding."
Now I haven't said anything to her. I'm sure she knows something is up with me, she can read me just as well as I can read her. And out of the blue this morning she says that she was doing a salt scrub (she's an Esthetician so this isn't out of the ordinary.) and it scratched her. I never broached the subject or gave her any reason to think that I know, so she told me this of her own volition. The weirdest thing about this morning and the only reason I'm still trying to hold on to trusting her, is that she acted perfectly normal this morning. She was lovey-dovey and sweet and it makes me want to thing that this is all in my head and I'm crazy.
Guys I don't know what to believe anymore. I so badly want to give her the benefit of the doubt and believe her, but at this point I don't know what's real and I don't have any solid proof that anything happened. And I don't know how to bring it up to her because at this point she can just deny everything and then I'm the bad guy for not trusting her.
I really just need some advice on how to handle this situation. I never thought I'd be dealing with this because of the amount of trust we have had in each other through out our marriage.
edit: I feel like I should clear this up. The only way she was masturbating, was if it was at Mark's house. She went straight over there after she got off work last night and I was with her after she got home until she went to work the next day. And I didn't sleep last night so she didn't do it in the middle of the night either.
At this point I am just waiting for her to get home from work. I still haven't decided how I'm going to confront her, but it's definitely happening tonight.
edit 2: Still waiting for her to get home. But I do need to say that I really would be absolutely floored if Mark's wife had anything to do with it. Anything is possible, but I feel like I know them pretty well. (But then again I thought the same about my wife, so who the **** knows). My honest guess as to what happened is that the wife invited her over, but as it got late, went to bed and left my wife and Mark alone. But there's only one way to find out. I'll try and give an update after it's over.

tl;dr: Things have been weird for a few weeks and I've found some things that point to her cheating on me last night and I don't know what to do.


Source.

LAWD lawd!