BOYFRIENDS

So, when I was year 9 (2010) I was seeing a guy in year 11. We were together for around 6 months or so, went to his ball ect blah blah. After that I lost contact with him. 6 years later (2016) he pops up on my 'suggested friends' list on Facebook. I added him, little did I think he would remember me or even accept me but he did. We got talking and I noticed that since me he has been with one girl. They had been together for 6 years, bought a house and earlier this year got married. The week I added him was my 20th birthday (Saturday) and I wasn't doing to much as I was flying back to England for 5 weeks. He asked if we wanted to catch up for a drink (Thursday), we did. He spoke about everything, and it was like we had never left each other's lives. I saw him again everyday till I left for my holiday on Tuesday. What shocked me when we caught up was that the girl he had been with all along had cheated on him and had told him that she was a lesbian (she now has a girlfriend).... Long story short he told me it was like I never left and he was so unhappy in that relationship and wants to completely have nothing to do with her, get a divorce, sell the house etc and be with me. We have been speaking since August and it's now November. He makes me so happy, and we get along like a house on fire (talk about anything, do anything around each other, no make up, etc etc) but I am still skeptical about how he's still legally married and what not.. He had asked me to be his girlfriend a few times and I've just said not at this time due to what has happened, though I do want to be with him.. What should I do?