Down in the ditch

I've been with my partner/ fiancé for more than 7 years now - we've been through tough times and good times.

My fiancé is severely depressed, so I support her wherever I can - I'm living together with her and her 9 year old son, who because as much of a son to me over the years.

A few days ago I found out that she was explicitly texting and exchanging revealing photos and videos with two guys she met while playing online games. She has been flirting with them for about 2 weeks, lying to me over that timespan regarding what she was doing/ who she was talking to, in order to mask those contacts. Obviously I'm devastated by that - we've been talking alot the last two/ three days but my bitterness and sadness doesn't seem to subside.

Today, after bawling my eyes out towards her I've felt a little better, so I decided to again engage with what we're usually doing in the evenings, which is playing video games together. I felt intensely depressed the whole time since she was talking to other people she met through the game while we were playing and I could tell that she wanted to charm them - here voice was at an high pitch and her affections were soft almost childlike - it was so so far off of her baseline. So I've struggled through my hour or two of playing, barely speaking at all and then I layed down in bed.

I have a bad feeling that I wont bounce back from what she did. I can't see her the way I did before... But breaking up would mean not only ending my relationship with her, but also, taking another intact family from her son/ my stepson. I hate this.