What kind of cheating is this?

My boyfriend (I’m a guy btw) and I have been together for three years. I know the term soul mates is thrown around a lot, but we truly were. In the last three years, we’ve gotten a place together, gotten two dogs, met each other parents, joined finances and basically share everything. We’re soo insanely tight we’re best friends as well as partners.

Tonight he told me he was going out with some co-workers from his new job. He said he was going to a wine-bar. The night before he went out with some female friends from his previous job, just to catch up. He’s been acting odd all week and really depressed, crying a lot. I felt a strange feeling that something might be going on. I checked our verizon bill (family plan) and there were several hundred messages to/from this one number I’ve never seen before. I called the number and a guy answered. When I asked who it was he said his name was Justin. My boyfriend then immediately called me and asked why I had called Justin just now? I asked him how he knew I called him and his reply was “because I’m sitting next to him”. I asked “Just him?” and he said yes. I then asked if he was on a date with this guy and he told me he was. I asked if he had sex with this guy and he said no at first. However, after pressing he said he did….once, last night. After losing it for about 30 minutes I called this guy back and asked him how he new my partner. He informed me that he had met him three days ago on Grindr (a gay hookup site) and had had unprotected sex with him three times now in the last few days. He also had no idea my partner and I were together. My boyfriend had told him that I was just some married guy that occasionally messed around with him.

I don’t mean to be long winded, but details are necessary to answer my question?...

How bad was this? If it was just once it could be seen as just plain lust. But, they’ve been together three times and the third night was an actual date (that he used to pay for with our joint checking account). Could such a thing be forgiven? I still love him very much but told him I never wanted to speak to him again. I’m asking what everyone here on fluther would do in my situation? What level of cheating is this?

Crushed.