Suspicion of cheating wife

I would appreciate advice from anyone on my current situation. I have been married for 17 years and have 3 beautiful kids. Over the past while my relationship with my wife has changed and I'm so confused. Bit of background, prior to being married (when we were bf n gf) wife was out with other guys and had some sexual encounters too. She has admitted some things but has never been willing to talk about it all. In December of 2015 my wife went to a work night out. She txt me asks by her to pick her up but the message was different from any she sent before. Usually she would ask me to txt or call when I'd arrived but this time she asked me to txt when I was nearly there! I arrived and went to see if I could see her. She appeared with one of her colleagues but did not realise I was behind her! I overheard a conversation which was something to with those guys we met, her friend then said don't worry about it it'll be ok! Her friend then realised that I was behind them and quickly halted the conversation. She then turned and said to me , look after her she's a good woman! Some pictures appeared on social media but quickly disappeared!! So of all photos taken on this night out my wife does not appear in any of them despite all others being in them! The ones she was in were taken down quickly. On the drive home she said " its funny what happens at work nights out". I asked what happened and was told it's none of your business! When we arrived home she txt her colleague "omg what did I do". Her friend replied her her are you ok? The following day I posed a question as I it appeared to look if she had no wedding ring on in one of the photos that! I also mentioned the photos that were taken down! Now if it had been me I'd have said "what photos show me". But she immediately phoned a guy from work and said where are all the photos from last night! Then came the wedding ring, now again if that had been me I'd have said I'd never do that to you, whereas she said if I'd have done that then I'd put my hands up......so again my suspicion was raised as she didn't say she wouldn't have done that. A few days later I attended a fair at her work and her colleagues that spoke to me before couldn't look me in the eye and avoided any conversation or chat! My wife's colleague posted on Facebook "I hate girls who take the c**t out of there better halfs" and two of her other colleagues liked this, however the two that liked it are in there little group of 4! My wife who always likes everything that her friends/ colleagues post did not respond by liking this post! To me it seems that this could be a cover as they know something happens that night! So, onto the next bit.... our sex life has declined significantly and there's no kissing etc etc ever! She no longer sends me texts like she used to or any messages of love! I asked her why she never says I love you when she's in the phone and she told me I will never tell you I love you in front of my colleagues and I'll not show affection in public, it'll never happen! I can see the point if I was a terrible husband but I work hard to pay everything and I do all domestic chores at home too which I think is right. I love her and always try to make her feel special in various ways. So over the last few years I noticed various changes deleting messenger from our iPad, hiding her phone etc! I also noticed various stains etc appearing on underwear whilst I was putting on washing! So I purchased the onsite semen detection kit and over the last few days I have competed an AP (acid phosphatase test and a PSA test on several items of underwear, all tests have come me back positive. The last 2 PSA tests showed strong positive in less than a minute. Can anyone provide advice on how specific and accurate these test are. To have all come back positive seems pretty substantial. I tested another garment just with the AZp and that came back negative, so I know the test ain't showing any stain as positive! Now I know that PSA and AP have been found in women but I am still concerned that she is having an affair! The quickness of the test turning positive was overwhelming! I'm now thinking of having a microscopic test and DNA test done on the garments at a significant cost, but this is the last confirmatory test. Does anyone think the AP and PSA test is enough (as the manufacturer says the PSA is 100% specific) or should I have the microscopic test done too? I'm absolutely confused, gutted and alone, so any advice would be appreciated. Thanks