Thank you Nighthorse, those are really great advice. Especially the communication bit.
I have to admit, invading her privacy was a major violation on my part. The initial "stumbling across" was literally stumbling across via text message on her phone while I was making a call, but the subsequent snooping that came from distrust were my doing, I feel very bad about it but I also knew that if I don't find out the truth, she'd lie to me for as long as possible.
I even went as far as writing 'T' an email to try to get clarification on nature of their relationship, but she instructed him to lie to me. He told me in email that nothing was going on between them, and that it was purely platonic, much like sibling's relationship.
As you can see, we lost a lot of trust from this affair, and part of me has a difficult time finding he room to trust again. I am forcing myself to, because I know if I don't, we won't be able to go on.
As for the hobby bit, I actually have quite a few hobby. Before all this happened, I was pretty wrapped up in extracurricular activity. GF and I hung out on weekends and some weeknights, but I definitely kept myself busy in the relationship.
My bigger issue is when she's out having sex with T and experiencing this great profound experience, I'm here at home and feeling extremely lonely, jealous and envious of T. I wish it's as easy as picking up another hobby, but at some point, I have to come home, to my empty bed, and with the knowledge that she's sleeping with him. I wish I can switch my brain off and stop obsessing over this fact, but somehow I just can't...
She's requested twice a month session with T. Given there's only 4 weekends a month, I suppose I'm only left with 2 weekends. Add weekends getaway with T on top of that, I just don't know if I have the capacity in my heart to move forward. I love her dearly, but I also cannot lose myself.